Please help with harassment messages?

I have this guy who keeps messaging me on different platforms. Usually he tries to add me on snapchat and I block him every time. He makes it pretty obvious it's him, plus I never add anyone so its obvious when it says searched by name. I have blocked him on my phone. On fb and on sc. Recently I got a new phone so I don't know this dudes old number or fake numbers he's massaged me on in the past and I have blocked. But recently since getting a new phone like 4 days ago I started getting messages from him. Im not sure if those numbers aren't blocked anymore or if he's made new numbers but I'd like to say something fake as fuck to him to get him to fuck off.. such as

hey I just saw this.. I think you have the wrong number my son/daughter is 13 she/he doesn't know how to handle these things yet. please stop messaging this number or ill be forced to go to the police for child endangerment/ harassment / predator.

Yea I need help I don't know what to say but I'd like to make it more to where they feel they really shouldn't message me anymore. Its been a whole goddamn year and this person hasn't taken a hint so I don't feel a restraining order will do anything. He'd probably just make up new fake numbers. He's too stupid to obviously TAKE A HINT
Please help with harassment messages?
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