Disgusting service

I bought a blackberry 9720 from FNB in August/September 2014 Accno:SDV***.I had the device for 3 months when it stopped charging. I have then returned the device to FNB Digital Planet and they have informed that they cannot fix my phone as it was repaired by someone privately. I have disputed this as I do know that the device is still under warranty, therefore would not have taken it to anyone else to fix. I have had a similar problem previously with another device that I purchased from FNB, that was also faulty the only reason why that phone was repaired is because it was insured. Till this day I have had to follow-up on the progress and they do not give me feedback. I am now paying for a device that i am not using and they do not want to repair. This device is now 7 months old and i have had no proper use of the device as it is laying at FNB Smartphone Operations. FNB device center gives pathetic service and a guy by the name of Shane sent me an email saying the device will be returned and if i want the device repaired it will be at my cost. Why should i pay for something that is still under warranty. I am very disgusted with their service.