iPhone warrenty process

I had an iPhone 6 which stopped working. I first took it to the iStore and they said it is hardware related and referred me to MTN where i got the phone on contract. I then went to the MTN store in Centurion Mall and they said that I must to the store where i got the contract. I went to Mall@Reds and they informed me that I have to go to the repair centre in Midrand. At the repair centre they advised me that they cannot book my phone in without the original contract that I sighed with MTN (Who keeps these contracts??) I said to them they should surely have a copy of the contract?? No they dont and they don't have access to the contract and without the original contract I cannot book in the phone?? Surely from a Customer Protection Act this is wrong? Anyway now I am stuck because MTN doesn't have my contract and I don't have my contract and I cannot get my iPhone fixed without the contract? Maybe I should just stop paying them and if they query it say I would like proof that we have contract??