working on a broken till while there are others!!

Around 8pm tonight at irene mall kfc I decide to buy meals and before I pay I decide to change my mind and asked for one of the meals i ordered to be voided then the cashier and the one that processes the void tell me that this particular till that I am beeing served on is broken and has a problem voiding items therefore nothing can be done so I felt forced to pay for what I asked to be reversed because the kfc till I am served on is broken. What gets to me is there were other tills that were not being used by anyone and I asked the cashier if those tills can void items and she gladly said yes. I am very dissapointed and angry that I was forced not to change my mind and pay for what I decided I dont need only because KFC 's one till is broken, is kfc telling me that am not allowed to change my mind. I have never received such bad service from kfc ever.if other tills are working perfectly and are not occupied why choose the till that is broken to serve customers ,so now it is my fault that a till is broken and kfc failed to assist and serve me accordingly as no solution could be reached. Its hard to believe that it is kfc that gave such terrible service.