CONTRACT ERROR - UNABLE TO RECEIVE MTN PHONE CALLS

I ENTERED INTO A NEW CELL PHONE CONTRACT WITH CELL C ON *** ONLY TO REALISE THAT I CAN NOT RECEIVE ANY PHONE CALLS FROM MTN SUBSCRIBERS. I CAN RECEIVE SMS'S & WHATS APP MESSAGES, BUT NO PHONE CALLS. A QUERRY WAS LOGGED WITH CELL C DURING OCT 2015 (REFERENCE NO SD432581) AS WELL AS SEVERAL VISITS TO THE CELL C BRANCH IN THE WEST COAST MALL, VREDENBURG (TEL: ***) THEY ARE UNABLE TO RESOLVE THIS MATTER.