Worst customer service ever

I have a contract with Cell c for 4 years now and recently my phone software crashed and i had to load new software from my computer to my phone were the settings was change and my phones automatic update was turned on. my phone updated 1 Gig of data and i got a bill of 1600 rand i phoned Cell c and asked if i can pay this bill in 2 installments and they said no i can not so i had to make a loan to buy food for the month. now i want to cancel my contract because i can upgrade but they say i am able to upgrade but not able to cancel. Cell c is a useless no care company and i will rather spend my money on a def-rend company who cares about their costumers i will make sure that every one i know with a Cell c contract cancel with Cell c