Mondo and Mtn service failure

Good afternoon, i have a long standing problem with MTN Mobile service provider and their agency Mondo. i erroneously app**** for a second contract and when i did return the mobile handset still sealed within the prescribed cooling off period at an mtn store. however it is now third month mtn has grey listed my original active contract stating that i should pay for the other contract. the bill has went up to over R1000 and i seem not to find any help. i have been sent from pillar to post by both mondo and mtn. i have called over 4 times until today mondo still gives me same story of them busy resolving the problem, on the other hand i am still paying my R260 normal active contract for a contract that's not working just to avoid being listed as non paying.