MTN - Missing Caller ID Issue - 3 Months later not resolved!!!!

On 10th June my contract was upgraded and on upgrading MTN deleted my CLI (caller line identity)!! I have not been able to see who is calling me or who I have missed calls from for 3 months now. For business, it's a nightmare. I have spent numerous hours of MY time on the phone and running to their stores trying to sort out THEIR problem. This is a massive inconvenience to me yet no one at MTN can be bothered to try get to the bottom of. No one seems to have the slightest idea how to fix it so they all just do NOTHING. They are happily taking my money every month and not giving me what I'm paying for. What do we do when you big corporations mess us around, keep billing us and send us from pillar to post?????