Im sorry but this report is invalid.
1) You set limits that only you can see.
2) you didn't warn him when he hit his limit, and decided to let him use 5 times his limit without letting him know beforehand.
3) You didn't set a limit, you only set a pricing for each GB of data used, that means you and only you know how much your customers are using, since most if not all websites that offer proxy with limits will display if you are near the limit or not.
4) He didn't blackmail you, he was clearly afraid of losing his reputation over this mess of a scam report that shouldn't even exist.
Tips:
1) find the way to warn your customers when they reach their limit or before they do.
2) Make it clear in the future that you will charge whatever they use, with a rate of 1GB / 8$. It's not even that clear and I've read your thread 20 times.
3) Calm down when a customer has a complaint, most times if not every time they are partially right. In this case, your customer asked you how to check when he hit the limit and you said you can send him screenshots every 10 minutes. Flash forward to now, you warned him when he hit 5.2GB (10 hours later). I think that if you are going to offer a metered service like that you will have to change your ways.
What will happen now:
I will remove every trace of trash talking / sales trashing from you thread as this was clearly a misunderstanding / lack of dedication from your side and his. He got mad, and rightfully so, and you got mad, thinking you are right, when you did things the wrong way.
Closed.