::steps on to her mental health soapbox::
No one, and I mean NO ONE, can cause someone to have a "chemical imbalance". No one can make another person go 'mental' unless the predisposition is already "in place". The belief that people "dish out isht" and that makes someone go crazy to the point of being a danger to others is complete bullisht and has no place in intelligent society. Wait, then, nevermind
::steps off::
Now, HotDamn, back to you.
You seriously need to get a restraining order. I have been stalked before, and in most cases that's what it takes. Also, check with your phone service provider. It's usually quite easy to have numbers blocked. If this still doesn't work (and I hate to say this!) but you might consider changing your number. And regardless of what some might say or what you even may be feeling you did not bring this on. This person is unstable and you need to get help from people who are trained to deal with this. I hope everything works out for you!