Poor client service from Cell C

I have been a Cell C client for approximately 20 years and never experienced problems with any upgrades. However I went to a Cell C branch last week for another upgrade but I was informed that I have an outstanding installment. I could not understand where this outstanding amount emanated from as my account is debited every month. The consultant requested me to pay the outstanding amount with immediate effect in order to clear the account. I obliged and to my knowledge the receipts were sent to the accounts department or whatever given that my dilemma was caused by the billing clerk last year from May 2021. Right now I am deflated since I went the extra mile to settle the outstanding balance but I am not getting any assistance from the branch as their hands are tied. They cannot move forward without acknowledgement of payment. So I want to know what the problem is. Has Cell C lost their sense of service excellence or what?