MTN ****s their customers

I have two contracts one with cell c and one with mtn. Both p20lites. Cell c dual sim works fine. Mtn has gone and blocked the dual sim capabilities. I asked the consultant at tygervalley store the day of taking the contract who co firmed the phone has dual sim capabilities so basically he **** to my face and MTN has ****med me. I can of course to flash the ROM to activate the ability but this would void the warranty. I was told i am getting a dual sim phone and thats what I want you ********