Cell C incapable of allocating payments made on their app

In November 2021 I , by accident, paid my Cell C account, twice. It is now almost 4 months later, and Cell C is still unable to allocate the second payment to my account, even after I send them my bank statement showing both payments, as well as the proof of the two separate EFT's done. The payments were done via Cell C's online app, that is directly linked to my Cell C account. Now they phone me daily , about an overdue account, as I did not pay January's account, because my account should be in credit. One cannot talk to somebody in their head office, but only to somebody in a call center. This is very frustrating. I am sure that due to this, I will also be listed by them as a bad payer, because the incorrect records show that I am overdue.