Cannot disable SMS roaming

I have returned from working in the DR Congo on Saturday. From Saturday I am unable to disable my SMS roaming. This makes that I cannot make any calls or used data on my CONTRACT! phone. I have used the Whatsapp chat and I have been to two MTN stores in my area without success. I get a message that a call with a reference number has been logged, but then I get another SMS that the matter has been closed. WITHOUT RESOLVING THE ISSUE! I cannot use my phone. I have restarted it numerous times and whenever instructed, but my SMS roaming is still active. I receive an error message when I go to SMS roaming on the *135# USSD code. Nothing works. I think is it ridiculous that calls and data is disabled EVEN IN SOUTH AFRICA when SMS roaming is activated. I will seriously reconsider renewing my MTN contract after this experience. It has been days without this matter being resolved.