Unsatisfactory Customer Service

On the 14 September 2020 I bought a phone for my son a Markham an A02 Core Samsung which is using mtn, now the phone is giving me a message on the screen which say IMEI:*** your SIM card cannot be detected from a service provider tha isn't supported. I phoned MTN call Center in December 2020 and they told me to go to MTN branch around where I live they will help me there , yesterday I went to MTN branch Hemmings ways East London and the Technician was not there, in which they gave me his telephone number to make an appointment for today. I phone him this morning telling him about my problem and he just Dismissed me telling me to take the phone to Markham with its box he can't fix it . I said thank you Sir will do.