Istore maponya mall is a ****

I bought an iPhone 13 3weeks ago,,, when the phone had to charge it showed signs of mulfunction, I paid 10500 and 300 extra for icare when purchasing it, when I take it back they tolf me I need to pay 12000 for them to fix the phone, I went to give them letter of demand the manager refused to sign I'm helpless and disappointed in their service Can I kindly get assistance my contact number ***