Refuse to repair device STILL UNDER WARANTY

On the 26 September 2015 I handed in my Galaxy S4 in at MTN Alberton to send to Samsung for the screen repair as IT WAS STILL UNDER WARRANTY AND STILL HAD THE 2 FREE SCREEN REPAIR WARRANTY FROM SAMSUNG.!!! I then on 07 October 2015 receive a sms advising me to pay R 2253.34... FOR WHAT??? AS THE DAMN PHONE IS STILL UNDER WARRANTY. So I call the number quoted and the damn idiot taking the calls tells me they will fix it out of warranty as they did not receive the proof of purchase????? HERE IS THE FLIPPING TWIST....I HANDED THE PROOF OF PURCHASE TOGETHER WITH THE BROKEN PHONE TO THE LADY AT MTN ALDERTON WHO SENT THE PHONE TO THEIR *****IC REPAIR DEPARTMENT. HERE IS ANOTHER TWIST, THE DAMN PHONE IS AN MTN CONTRACT PHONE ... HOW CAN YOU NOT GO AND CHECK IF THE PHONE WAS UNDER WARRANTY AS MY DETAILS HAS BEEN ON YOUR SYSTEM FOR YEARS. THAT IS RIGHT I HAVE BEEN AN MTN CUSTOMER FOR OVER 15 YEARS AND I HAVE TO DEAL WITH STUPID PEOPLE WHO DOES NOT UNDERSTAND THEIR OWN SYSTEMS. Then the idiot who takes the repair centre's calls tells me they don't accept the proof of purchase after so I will have to pay. WAY TO RIP PEOPLE OFF MTN!!!! While trying to sort MTN's f@*kup o