Unacceptable service

I am not happy with the level of service I have been receiving from Cell C. I have been a Cell C customer for many years with absolutely no issues until now. I have been trying to do my 24month upgrade on my 2 contracts since December 2021, yet it has been nothing but unnecessary , aggravating issues. I was advised by the staff at the LBM store that my account was blocked due to an outstanding amount which is already a red flag as my contracts are debit orders that have not bounced! After many back and forth calls to Head Office, being told in fact my account is clear, then it’s not, then it is, then it’s not, it came to the fore that it was an amount outstanding from 2018 on an old account (previously Glo Cell before they were taken over by Cell C) before I migrated to Cell C. Never mind that I was able to upgrade my contracts in Feb 2019! I made the payment of the apparent outstanding amount in order to speed up this process, sent the proof of payment to all involved and I was assured all would be sorted and I would get my upgrades. They have now allocated the payment to the complete wrong account and I am still unable to get my upgrades! If they can allocate payments incorrectly, how can I be sure I even owed them anything in the first place?? I am now at my wits end and would appreciate CELL C sort this out as a matter of urgency as this is unacceptable!