2 Months to repair phone

I bought an Apple I Phone 5s from FNB and it was defective after 2 weeks. They collected the phone for repairs in October last year and I still have not received a repaired or replaced phone. I wrote a reveiw on hello peter.com 2 weeks ago and the same day someone phoned me and told me the complaint has been escalated. That was the last I heard from FNB. I wont recommend anyone buying FNB smart device's. If something goes wrong you sit for months without your device. And they dont miss their payments no they take their money every month. This is the most pathetic service i have received in my life. Had to go and buy another phone. Does anyone have a suggestion on how I can escalate this situation?