******* with card payments

Please tell me how it’s legal for Uber to take more money out of your account after a trip? Then they say but the traffic plays a role etc but if it was a cash trip that wouldn’t have happened….how is it even legal to take more money after I agreed to an amount? If I knew it was going to be more I wouldn’t have taken it, I took the trip because I could afford the amount advertised, nowhere does it give an estimate of what the amount could be…why must I pay more because uber miscalculated the fare beforehand and offered it for less than valued…why is it my fault? Agin if I knew I wouldn’t have taken the ride…this can’t be legal .