Harassing calls for a Cell C account that was paid last year - took on the claim without knowing what it was for

I had an outstanding amount stemming from issues with Cell C billing during 2020 hard lock down. They handed me over to VVM at the time and after months of requesting info in Dec 2021 they eventually sent me invoice/statement showing where the amount is due from; I paid VVM in full within 24 hours of receiving the invoice/statement and send the POP to both Cell C and VVM. 3 weeks ago I started getting one or more calls almost daily from SSDA claiming I owed Cell C money. Each time it was a diff amount they claimed I owed and no-one had info as to what this claim pertained to. After two weeks of me asking for info for this claim I received an invoice that I had already paid VVM. I sent the POP to SSDA days ago and am still getting harassing calls and sms claiming I owe Cell C money. Yesterday alone I received 2x emails, 2x sms and 2x phone calls from them.

I would like a formal apology from Shapiro Shaik Defries and Associates (SSDA) for taking on this claim without any evidence or information to what the claim is for and I would like them to promise to not take on any claims going forward for anyone if they don't have supporting info pertaining to the claim.