Why is it people don't understand why we call? Is it because we don't explain it? Or does the need for evasive action so occupy them that it doesn't register? Or both? I'm not really sure.
At any rate, you always hear of folks in a panic because the same JWs keep coming back and they don't want them to. How did those Witnesses get it in their heads that they should keep visiting this or that home? How do you get rid of them?
Tom Wheatandweeds got such a letter from a householder who almost felt stalked! Why do they keep coming back, she fretted. I mean, sure, that first visit was kind of fun. "I went to religious schools as a kid and I'm familair with the Bible," she said, "though I don't believe it. That first chat was interesting, but I never meant for them to come back again and again and again. Help! I've explained to them that religion is very personal to me and I've told them that I would never convert. It makes no difference! They keep coming back. Maybe I'll have to move!"
Wheatandweeds, nice fellow that he is, wrote back. With his inside knowledge he knows how to get rid of them. He knows what works and what doesn't work. Barfendogs also knows how to get rid of them, but his suggestions are crass and rude, and most people have too much class to use them.
Don't speak to them about religion being too personal. That strikes them as an un-reason and they can't get their head around it. They think of Jesus and the disciples talking to anyone under the sun about religion, none of whom said it was too personal. Seemingly, that's all they did back then.
Don't speak to them about converting or not converting. That is not their goal at this point. It may be months down the road, but it is not now. Now (from their point of view) they want you to build a base of Bible knowledge, and they think they can help you do that. Only when that is done can a person make any reasoned decision, yes or no, about converting. Most people who study the Bible with Jehovah's Witnesses do not convert. They know this (or should) and it doesn't matter to them. They are happy just to teach the Bible, viewing that as their ministry.
Look, if you don't want it, you don't want it. Several visits is enough to say you've looked at something fairly. You don't even owe them an explanation. You might choose to give them one, out of courtesy or whatever, but you don't owe them one. Your time is yours. They are misreading the situation. Maybe because you are sending mixed signals. Maybe because they are not very discerning. Probably a little of both. Explain how you feel. Showing them your letter might help, if you choose. Why not?
On the other hand, knowing their m.o. might allow you to take advantage of what they offer, if you want. Tell them, not only do you not want to convert, but you will be absolutely furious if they ask you to do that months down the road. With that understanding, yes, you will study the Bible with them for a limited period just for your own gratification. 3 months, 6 months - you set the time period. And then it's done. They have a book, they must have shown you, entitled What Does the Bible Really Teach? that they use in studying. They are pussyfooting around trying to ease you into such a study. Tell them to stop pussyfooting and get down to it. One chapter a week. (two weeks at most) That way you cover ground and aren't wasting time. You can always reassess at the end of the time period if you like.
Studying the Bible with them will show some things in a different light. You mentioned you became familiar with the Bible from Christian schools but don't believe it. A reason for this is that most church teachings are not found in the Bible. It is the attempt to read them in that causes confusion and makes people discard it all as nonsense. You may not agree with things JWs say. But it will be different from anything you have learned in the past.
So there. That's what you should do. Either cut loose completely and don't waffle, or take them up on a study for a limited period. But do one or the other and end this frustration. No need to think about moving! You probably like your place.