Bad service

I have a contract with telkom suddenly i can't received calls from other networks providers i only receive from telkom, when i get a call from other networks it got cut within the first 2 to 3 seconds of the call, i tried to go to telkom stores at Alex mall near me but they couldn't help, i tried lodging a fault through on line but i can't get help, am stuck with telkom as i can't cancel the contract before 24 months. Please help me resolve as i had to get another phone number so that people might able to call me