WORST SERVICE FROM MTN

We pay every month for MTN via EFT at about the same date. Since November our phones are being suspended every other day, when we phone MTN to find out what the problem is they tell us that we are overdue with our account. When we ask which month we didn`t pay, it is always a different date. We have sent our proof of payments through to MTN a lot of times, but still our phones services are being suspended. We are really sick and tired of the service we receive from MTN. Today again our phones are suspended, after we sent the proof of payments again. When my fiancé phone them now, they have the excuse that their systems are offline, they can`t help him. He must phone back in an hour. I don`t know what to do anymore.