INTERNATIONAL ROAMING DEACTIVATED

At the end of April 2015 I upgraded my contract. Previously my international roaming was activated. When I upgraded I specifically asked the person dealing with my upgrade if it would work. It was confirmed that it would. Two weeks after my upgrade I was in Lesotho and my roaming was deactivated. I called the person who assisted me with my upgrade from a landline and so my roaming was activated. however, I can now only send and receive sms when i am abroad. I CANNOT MAKE OR RECEIVE CALLS. This is frustrating, I am a business women I need my phone when I am abroad. The company I work for is losing it because nobody can get hold of me neither can i make calls. I have reported this problem to a few mtn stores i have also called the call center. This problem has still not been resolved. I need an urgent response and preferable a positive one. I will not recommend anyone to get a contract with mtn neither to change networks due to all the drama that does not get resolved,