Frustration from MTN

I have a contract with MTN and I don’t use their SIM card on my phone as I used my previous number with Cell C. I decided to port from Cell C to Vodacom and I haven’t been able to make or receive calls and SMSes ever since the port. I went to MTN to report it. I was told my phone was blacklisted that’s why but they are unable to tell me why my phone was blacklisted and by who because I did not report it lost or ******. They said to me the blacklist is removed and it should work but it’s still not working. I went back to the store and the consultant called her head office. She gave me the phone to speak with the agent on the phone and I was told the underwriter has found fault on my phone and they agreed to give me a new phone but I must pay and excess fee of R300 firstly. I wanted to pay but I decided to call MTN and find out what’s happening and what fault it is they found because they didn’t give me much information. To my surprise, the agent I spoke to could not pick up my ID and cellphone number. I then gave him the reference number I was given and told me it belonged to someone else. Now I had to go back to the store and tell them what happened and the consultant had to look for my reference number. She looked into my incident and told me my phone has been fixed and my phone should be working but I showed her it’s still not working. She gave me another reference number and when I called the agent told me to switch my phone off for 48 hours and it should work immediately after that. I’ve switched it off and it’s still not working 48 hours later. Imagine using an iPhone X that cannot make nor receive calls yet I pay R879 on a monthly basis.