Does The Warranty Service Exist

I have a business contract with MTN and one of the phone's is faulty cell number ***). I think it is a software issue & took it to the branch in La Lucia Mall. It is still under warranty however the branch has advised that there is a cost to have it inspected by their repair centre in Jhb. I was also informed that it will take 21 working days to have it couriered to their Jhb repair centre for this to be done. I have also tried to contact the customer care to advise why this is so & have not received a response. Why is there a charge if the phone is still under warranty?