Why extra money for an Uber ride?

Used Uber for the first time on Saturday, 14th of March. Got the invoice and paid. After been dropped -off, all of a sudden they consistently deducting an extra R31 and every time they're trying to deduct, R1 fee goes off - since I've put my online payment to R5. How can they afterwards change to a higher amount, although you didn't take any other alternatives. Why is it that a lot of companies want to abuse your account when they have your banking details - totally unacceptable. Never ever making use of them!