Let's consider what won't work to stop the calls and/or mail. If you politely request that they stop calling you or sending you mail, that you are no longer interested in Scientology, that probably won't work.
A perfectly reasoned approach, telling them that you didn't get anything out of the auditing or courses you took, or have some doubts about the legitimacy or goals of Scientology, most definitely will not work. Of course, then they will just to sucker you into courses that WILL work, they think. That could result in more calls.
I suggested that you tell them you are seeing a psychiatrist. I think this is a much safer lie than saying you are using drugs or even an active critic, who reads and posts on ESMB. They can't really use it (that you are seeing a shrink) against you, or tip off the police that you're a drug user (when you aren't) or try to interest you in Narconon.
Throwing a fit and using foul language about what a money-sucking scam Scientology is, without threatening anything or anyone, could also be effective. Saying something like, "Wake up! You're in a fucking cult started by a fucking science fiction writer!"
I had a friend who took only one course decades ago and then got a flurry of phone calls from them decades later. He thought he was being very clever, by being polite but acting kind of naive about their motives, and holding lengthy conversations with the caller about off-topic things like politics, or Scientology's business model, which he thought was flawed. He considers himself to be a financial genius, when mostly what he did was hire smart financial planners to invest the heap of money his parents left him.
Never mind that the caller was someone that was usually young, and didn't know who the VP or United States was, and had no idea what he was talking about, he was trying to show them how much older, experienced, and well-educated he was compared to them, so that they would obviously see that he has no interest in goofy stuff like Scientology. He wanted for them to appreciate how smart and experienced he was -- like he was beyond Scientology.
This didn't work at all. He wasn't even telling them, "Don't call me! I don't want your damn phone calls!"
The initial call from them was that, "Hi. We're just calling to verify your current address?" He wouldn't verify his address. This made them call 20 more times in the next months. He wouldn't tell them why he was annoyed by this.
Finally, one day he lost it. They were doing things like calling him back after he hung up on them. He just started swearing at them profusely, telling them to "fuck off" and a lot of other things. They never called again after that.
Before that, I kept telling him to stop beating around the bush with them, or trying to reason, that these people are stewed in cult juice and won't even understand you unless you directly and rudely tell them to fuck off and that you don't want their phone calls, and that you'll contact a lawyer if they persist.
His experience was worse than yours (the person who started this thread). The auditing and training routines he did during his initial course package made him feel worse. He realized all the rumors he heard about Hubbard were true, and that they were probably raided recently (it was just after Snow White when he took his course) for good reason.
Instead of getting love bombed, he thought the staff were creepy, and that some of the students in his class were unfriendly and peculiar as well. No one had questions. It was like they were there to be indoctrinated without even understanding what was going on or why they were doing it. He had to make a scene at the org to get them to stop flooding him with junk mail after the course was over and he made it clear then he wasn't interested in another.
I understand why people like yourself get wishy-washy about this type of call. But I think you have to understand why this works for scientology, and how successful they are are suckering people back in. Even when people don't get anything out of it, the same hope that they went in with, that it sounded so good, may still be there in part. Even if they only get one in twenty back in for a course, that could result in lots of money if that person ends up stuck in it for decades.
What pisses me off about it, is that by being polite or overly vague, whether out of fear or whatever, then the people making these annoying calls never get a clue! Instead, they feel masterful and superior about manipulating people. They think of it as trying to help, and the special power they have.
I would like Scientology's street business especially (E-metering, offering personality tests and selling Dianutty) to take a huge dive, as more people become bold enough to tell Scientologists to fuck off or inform them they are selling a scam.
"Would you like to take a free personality test?"
"Is this Scientology??? No, fuck off -- Scientology is a trap. Haven't you seen GOING CLEAR?"
That's all that has to be said. Of course, they are looking for the vulnerable, interested people, so you probably have to look vulnerable or interested to be offered to take a personality test.
Of course people like Tory are the ultimate, but there are too few like her to match their outreach at all kinds of flea markets and everything.
Anyway, I think former members, who have no family stuck in, even if you just took one course, should be very pointed and clear with contact from the cult. Ultimately, you're doing that for yourself and to help them. At which point it becomes really uncomfortable and unpleasant to try to "reactivate" former members, that's going to give the people doing this work some reason to think about what they're doing.
Chris Shelton talked about how good he was at recovering former members, and of course, he thought he was helping people. Well, maybe if when he called people, more people, the ones who didn't cave in, had been really honest with him instead of so polite, vague, or sponge-like, he would have gotten a clue a lot earlier.
Before there were cell phones and everyone had a land-line, and before there was a place you could go to reduce sales calls by putting yourself on no-call list, I tried various techniques with sales calls.
With the people who seemed to have a long spiel about their water-filtration system or whatever, I would just put the phone down and let them chatter on for a few minutes until they realized no one was there. It felt good for me and was quite effective.
I don't know if that would be a good technique to use on Scientology but it would be funny. The second you know it is them, either hang up immediately or put the phone down and let them talk into space. They aren't worth talking to.