Future mother in law issues. Please help!?!

Sorry for the length.
My future mother in law hates my guts. Her son and I have been dating for close to 3 years. He proposed to me on our anniversary in December and since then she has tried to find anyway she can to break us apart. She blocks my number, puts restrictions on his phone. She has tied everything possible. 
My fiancée just turned 27 and I'm 21, which isn't that big of an age gap at least not for me. So anyways, my fiancée came to visit me while I was away at college in April and she was so irritated with the fact he was spending time with me that she drove 6 hours to try and break us up and drag him home with her. She sat in the parking lot at my apartment for 8 hours just waiting for my fiancée to come out and talk to her. I went eventually went out and talked to her and she went crazy on me. She demanded I give her my engagement ring because my fiancée bought it with a credit card so it belongs to her. (I know for a fact he didn't because it's just a cheap ring that in my option doesn't look cheap. I'll add a pic of it at the end) She then grabbed my hand and tired to pull it off my finger.
About a month and a half ago I had a miscarriage, and my fmil found out and has been calling and texting me telling my that I'm lying that i didn't have a miscarriage that I'm just trying to take her son and husband away. (My future father in law things of me as a daughter he never had.) And I'm at my wits end and don't know what to do any more. Any advice or anything you want to add would be much appreciated.