Mum invading privacy

My mum went into my old phone when I was at my dads place and through my messages with this guy who I had been sleeping with (so you can imagine what was in the messages). 
She then told me days later thinking I am emotionally unstable and that letting a guy treat me the way he did meant something wasn't right. At that point I was just shocked but was thankful it was only those messages not others as well. 
What really got to me was when she decided to message him and tell me how he has no respect for woman and to keep away from me and other girls. 
I don't know what to do! I don't know how to act. She has no right to go through my messages and especially no right to message him. 
I need advice. I am so hurt