Try for a restraining order but this might well prove fruitless as he's not making an overt threats, trespassing or turning up in odd places. You at least want him on the police's radar in case things turn really nasty.

You could also take legal advice. Maybe a 'cease & desist' type action? Even if it's frivolous the prospect of having to defend yourself in court and the damage to reputation that such an action could cause even if it goes nowhere might make him stop.

Never reward a stalker with any communication. Your nice 'no thanks' are just you playing hard to get in his twisted view. He's had you before so as far as he's concerned it's just a case of finding the right approach to have you again.

Change your phone number, social media and go dark. Buff up your home security and have recording equipment.