Poor service by MTN

Good day, I would like to log a complaint with MTN. I am a contract client and just did an upgrade last week. Since Monday I am un-able to make out calls. I called their call center from Monday bt till today no joy. I also logged a request via their twitter handle MTN service where I was asked for my details and even SIM card numbers bt till today I am still experiencing the same problem. As a paying client and one that has been there with them for long this is unacceptable. I am even thinking of cancelling my contract as I cannot pay for a service that is not rendered. Their service is not just poor bt non-existence cause of u say poor u mean there is a little chance. As for the call center agents they need training on customer serve