I can only say one thing about this:
If at all possible, NEVER work somewhere that you are not wanted. You will be miserable and they will find an excuse to fire you as quickly as they can.
My guess is that the 'problem' is you organized their department and your former Dept Mgr felt threatened by your ability and popularity. Their may or may not be some nepotism with regard to the person hired after you and her friendship with HR manager. It's sad, but it happens all the time. This is not your failing, it is theirs.