unfair treatment

I bought a cellphone contract with fnb, then at a later stage it gave me technical problems and I consulted with them and they advised me to take it to i-fix. It was then booked for repairs, got a call to come fetch and hardly in a week time started not working again. I went to the branch after, we then phoned the device department and I was told it was faced out, I have to choose another phone. After conclusion I was told the courier will ship the device, and it was done unfortunately I was at work and my cousin signed for the device. In a weeks time the same Ram courier came back to fetch the faulty device and I gave them the device yet didn't sign any document or receive any proof. Late 2017 I reliased that on my fnb profile it shows two devices, I then asked, followed up with the device department on a weekly basis and the answer I got was they have escalated the matter then early this year the whole process was carrying forward since I never got a respond from them. One day when I phoned one of the consultant told me they need a proof, of which I don't have or didn't receive from the Ram courier. They claiming I still have the faulty device with me. The issue is I'm paying for something which is not in my position