Fnb should not sell devices

I took a Samsung galaxy S7 edge out on terms with fnb in 2016, the phone retailed for about R17k at the time, when i got my phone i knew there was a battery issue and emailed and called only to be put on hold, i gave up as i had alreadt sold my previous device , now 2 years later due to this battery issue my battery has swelled to a point where the case is loose. These new phones are not like the old ones where you can open it up, I once again emailed explaining that they should not call me as each time my phone rings it dies even when on silent. So now im sitting with an expensive broken phone that looks brand new, not a single scratch on it, and i cannot use it because you guys dont check your devices . I explained why i stopped paying you , it was literally like 4 or 3 months before my last installment which means you have received almost 95% of the outstanding balance, now you want to add to my balance due to non payment and give me almost R5000 to pay???? For a broken phone???? Why is it so hard to send an email? What are you going to do to fix this issue? Should the phone happen to bomb up in my face will you take responsibility??? Im waiting fnb , fetch this defective phone and replace it or remove that damn balance