This isn't a credit card error. This would be like signing a contract with Sprint for 500 minutes a month for $20, getting charged the $20, and then being charged an extra per-minute fee that wasn't in the contract.
Kind of like when you get your latest Comcast bill, Sprint bill, natural gas bill and see that "effective $DATE we will be increasing our price by $X% due to $Y". Happens all the time unfortunately.
It doesn't happen like that though. Natural gas, sure. Power bill, definitely. I've never had natural gas or electric service where I entered a contract for a service at a fixed price. My cable and cell phone service are on a contract, they can't increase the cost during the contract period.
