My phone was sent for repairs and now lost in transit

Hello Peter I sent my phone for repairs in November 2018 and after several follow ups with them they told me that my phone was lost in transit. I sent several emails trying to know and understand what is going to happen but they are ignoring my e-mails because the courier told them that MTN is suppose to replace the phone.I sent the phone to MTN for repairs because the phone was still new, I bought it in October 2018 and sent it for repairs in November 2018 which was not even 1 month.I paid for repairs but now they are ignoring the fact that my phone is lost. They are not bothering themselves to tell me what's going on.I have been MTN customer for more than 20 years on contract.Now they treat me like this.The worse part they are debiting my account still while I do not have the phone.

Please assist