no calls but data works

I got a new sim from telkom mobile. it kept saing phone cant make voice calls. my data works but i dont get 4g.. i was told to get a new sim, did the rica process and still have the same problem 2 weeks later. i cannot make or recieve calls. yet my data works fine. when i contacted telkom i had the worste customer service and all they could say was buy a new sim, that will be the 3rd one. this is so pathetic !!!!!!!