Iphone 6S Battery Swelling

I took a contract in February 2016 for an Iphone 6S and the phone has battery problems, it keeps switching off and the battery swelling. On the 4th of April I took it to the MTN Tyger Valley branch where I signed up the contract and it was booked for repairs and i was told that they would give me a new phone after assessment which should take up to 7 days. On the 8th of April, the agent Tamlyn phoned me to deactivate \Find my iphone\" which was done same day. Two weeks down the line, I phone the repair centre and they tell me that the phone is not in their system and it is still at the Tygervalley Store. I went to the branch and they apologised but up to now I haven't heard from them. What kind of service is this??????"