Ubereats

I placed an order to KFC and on the app it showed they had street wise 3 pap I ordered then few minutes later they called and asked if they can.swap pap with chips I said no I want pap I was advised that I should cancel my order since there's nothing they can do so my question to Uber eats is that why am I being charged R127 for cancelation instead of they store because how can they claim my order was already processed yet they had 1 item missing?