This woman is really pushing my nerves.?

So, this stupid ex-friend I has does graffiti for fun and I guess as a outlet for his creativity. But I yesterday, I was talking to him about graffiti and he was telling me about it, and asked for ideas. So I gave him ideas, and he told me whatever. I didn't take it seriously though, and I was like whatever. So later that night, he starts constantly calling my cell phone and I ignore them all. Today he was calling me again and this morning until I finally answered and heard his mom start talking and she sounded angry so I hung up. None stop she's been calling me, and I've been ignoring the calls only to get voicemails. So I listen to them and she is angry saying: I need to talk to you and that she needs to talk to my parents, and that she iis going to call the police on me about the graffiti. She needs to stop before I explode, I'm not responsible for her sons actions, I've never committed a crime in my life and I can't control what he does. What do you think?