Hi, it must be really difficult having your mum intruding in your life, dredging up a lot of things I'm sure you'd like to put behind you. Have you stopped asking her not to contact you- if not just completely cut off communication with her (she should know the score by now) otherwise you're just going to be giving her a reaction, which she's looking for.
Could you go to the police describing the situation and citing it as harassment- they may have a word with her at the very least.
Do you think a counsellor will help with some of your feelings- if you aren't already seeing one- your doctor may be able to refer you, inc. sounds as if your aunt may be there to support you if you discuss this with her too. Your aunt may even step up for you to your mum again if you tell her about it?
Sorry if this isn't that helpful, just trying to think of some ideas.