Since you did the letter method (something I always warn using for several reasons), you should maybe first check back with what you wrote or asked or offered in your letter. Maybe you will figure out, that the things you have been asking back then, may not exactly what you want now or can be even be differently interpreted? At least that, before you go ahead and say "It's the succubus fault..."
Because, that's kinda the impression you give here, like pushing the fault to the succubus.
Regarding your questions which stay unanswered from her, maybe they are not for you to know the answers, maybe they are not relevant at all (the way she sees it), maybe they are the wrong questions? I don't know what you are asking and getting no answer, but you should consider things like these. Especially, since you say you are shy and don't like to talk.
How about, you try to be first honest with her - I mean, speak with her about your desires, your emotions, your thoughts. And then, if you get nothing back, if you do all these things, maybe as last resort (only), consider, that you have called a spirit that isn't for you and move on.
Like it was said, it could be also a spirit, which does have no good intentions with you. However, nothing in your post seemed to show, that she is doing something bad.
A male chatting with his succubus:
- You know, you are ridiculously attractive for a devil woman.
- I know, but thanks for saying so. Devil women have feelings too!
- Are you ... going to kill me?...
- Yes... but you'll enjoy it!
- ... ok!