Sorry for the incident.
It is always better to avoid going to the boy's place or bringing him to your home/hotel.
If you bring him to your home/hotel make sure the lobby will get his ID info.
It is better to go to a sauna or a motel.
The guy is clearly a scammer. One could say you lost the bill but to charge 50 reais more for a 100 payment is absurd! It is quite normal that boys charge more for a credit card payment. The transaction fee can be as high as 5 to 10%, but 50 reais was way too much.