I went through much the same situation but there were children involved. My suggestion, regardless of whether there are children involved, is to let your family and friends, your ex and even your employer know what is going on. Ask them to please not discuss you or your relationship with her, to let you know when she contacts them, and to ask her to stop contacting them. She’s only texting/calling and talking about this to people who will listen. Tell your mother to ask her to stop calling and to hang up. If she continues to call, she can contact the authorities about harrassment.
Everything that is written down, keep it. Keep records of everything said and done. Either record the conversations or get copies of the text from the phone company. If she’s writing your brother, have him send you the letter. If she’s calling you, go to Radio Shack and buy a recorder for the phone. They are around $100 and they have one for cell phones too. It is legal to record a telephone conversation in NC as long as one party knows it’s being recorded. You may not ever need the records, but I felt better having everything documented in case anything happened to me.
If you’re worried about what she may be telling people, I’ve learned that unless you’re willing to go so far as to get a restraining order or take her to court for slander or libel, your best course of action is to ignore her. Slander and libel must be proven in court to have effected your employment and/or your way of life and that they did it with that intent. Unfortunately, it’s a long process for very little satisfaction. And restraining order will not keep her from talking bad about you to anyone who will listen.
People who know you and your boyfriend will know what is true. If she’s acting crazy and calling everyone just to spout wild accusations and create drama, then think how it looks to everyone else. They know you, they know your boyfriend, and here’s this other person that they don’t know contacting them. If they know ahead of time that this may happen, it’s easier not to get upset when it does. And I’ve found that if you ignore them, it takes away their power.
I wish you the best of luck and keep in mind that if you two make it, it does get easier.