Bad Service

My Husband bought a Samsung A53 Cellphone through a contract with MTN. The cellphone's screen went black middle of January and since then we are struggling to get it fix. It was send in now for the third time and it seems that between MTN Caledon and Samsung in Johannesburg the cellphone disappeared completely now. Nobody knows where the phone is and we struggle to get some answers from both companies. We are paying for this contract every month and please want some answers!!!!!!