Bad service MTN

I upgraded to the Black Friday Diamond data package in November 2023 wich you are supposed to get 400GB/mth. MTN only gives me 300GB/mth. I have called every month and there is only promises that the problem will be corrected but it's not. MTN don't inform you about the problem which they know about. MTN don't give you feedback. MTN don't reimburse you the lost data which is 400GB. I don't know in which industry is this ecceptable.