Bad bad bad service

Soo i oderd food from uber eats and before i checked out my amount was R73.20 because it said it was a premonition and after entering "place order" the amount changed to R138.20 as we can't cancel the order we had to pay... My ISSUE IS WHY DOES UBER EATS CHANGE THE AMOUNT THAT NEEDS TO BE PAID AFTER SHOWING THE PREMONITION AMOUNT