MTN SLACKS TO ACTION UPGRADE FOR 5 MONTHS

I have been trying to action an upgrade since October 2023, I have been in contact with MTN to first action a credit limit increase so I can then action the upgrade, however, no one can assist me. I have called numerous times, I have so many different reference numbers from MTN for each call that I have made and I still have no responses to calls or emails. So what is the problem. Why can a simple credit limit increase and upgrade take 5 months to complete.