Contract paid but no paid up letter issued

The service is very bad I don’t even know what to do with this query coz I have been transferred from pillar to post it seems like no one I willing to help me. All I need to do is to make peace with the fact that I am stack with this query. I will never have anything on credit because of MTN but that time I don’t even owe them a cent. I don’t know if I should say is the right choice to take contracts with MTN or what coz wow 😭😭