I was pestered by a seller a few years ago and I messaged them asking that they stop contacting me. They continued to send messages so I sent a 'cease and desist' message informing them that if they continued to contact me I would fill up their inbox.
My message was ignored and I received yet another message from them, so I sent 10 'Stop contacting me' messages, then 20 the day after and 50 on the third day.
I didn't hear from them again.