I've had this happen once in the last 5 years in the US. A server changed the tip/total for $5 more. It was on my list of things to complain about, but I never did. The restaurant is out of business, so I guess they got what they deserved.

Generally, I'd call the restaurant, and ask to speak to the manager. If you don't get satisfaction, then issue a chargeback. Many credit card companies charge $10-$30 for any chargeback, so it will hurt the company, for sure.