MTN - being made to pay for phone which is not working

I submitted a claim to insurance in August 2020, which was declined with no proper valid reason. I'm paying for a contract including insurance monthly but my phone is not working properly. I was told to take my phone to an MTN store so it can be booked in under warranty, when I arrived at the shop I was told they can't assist me I must do an insurance claim. I'm vey confused and need answers urgently as a paying customer.