Home wrecking whore won't go away

My fiancé cheated on me about a year ago. It took a lot of work but we have been working things out. Today that stupid cunt texted his phone. I'm furious!!!!!! She got a new number and texted him like what the fuck? What gives her the right to pop the back up whenever the hell she wants? Advice on what to do because I'm about to go burn her house down. 
Edit: no she hasn't texted him until today; from a different number he responded saying "who's this" I looked up the number and found out it was her. His solution is just to block her new number but that's not good enough for me. This bitch wants to play games