UNHAPPY WITH MTN

SOMEONE FROM MTN PHONED ME LAST WEEK AND SOLD ME A 30G SIM CONTRACT AND I TOOK IT. ON MONDAY TWO SIM CARDS WERE DELIVERED AND THEN I PHONED MTN TO ACTIVATE THE SIM CARD AND FIND OUT WHAT THE SECOND ONE IS FOR, I WAS TOLD THE TURN AROUND TIME FOR ACTIVATION IS 24 HOURS. TODAY I FOLLOWED UP BECAUSE THE SIM CARDS ARE STILL NOT WORKING ONLY TO BE TOLD THE 30 GIG IS 20G YOUTUBE DATA AND 8 GIG NORMAL DATA. WHEN I WANT TO CANCEL I AM BEING TOLD THAT I NEED TO PAY A CANCELLATION FEE. NOW THE QUESTION HOW CAN THEY EXPECT ME TO PAY A CANCELLATION FOR SOMETING I DID NOT AGREE TO BECAUSE IT WAS BROKEN TO ME.