Can't call MTN numbers from Cell C

Cannot call MTN numbers from Cell C! If you have had the same problem please comment. On a good day I will try and call an MTN number and it will connect, then immediately after hanging up will not be able to call the same number as well as other mtn numbers for days on end! Apparently Cell C doesn't actually care! Their service is absolutely disgusting, weeks of phone calls to customer care trying to resolve this issue and according to their system, their story is that either there is no problem, or I must enter a code-which doesn't work or my favourite is that the issue has been resolved-obviously not if I am still calling to complain. I have even been in to cell c where the problem was acknowledged as a network problem and escalated. It was also apparently resolved with a solution entering a code that doesn't work either. To date not a single string of feedback on all my complaints even though I have been told that someone will be contacting me back. I actually work with two other people using different phones and different contracts both with exactly the same problem. Completely unacceptable. I cannot wait for my contract to end to leave this BS network!