First of all I'm sorry this happened to you.

What do I think you should do? Just move on and try not to think about it anymore, report it on the providers section and as soon as you post that just forget about it.

Just like in any business, every once in a while there will always be someone trying to cheat/take advantage of the other party... this happens to someone every single second and you shouldn't let emotions get in the way... let him threat and say whatever he wants... just cut all communication with him.

These situations are inevitable to happen in any line of work... if you open a store people will shoplift... if you open a restaurant customers will dine & dash or return food or complain about something bs... it happens on every single line of work... even to doctors and lawyers... etc.

I used to own a small advertising company and customers would always ask for more than what they had originally paid for... the same for the type of business I own now.