BAD Service

I went in December 2022 for Rabies Treatment at ER Consulting in East London. All my bills was paid on the 17th of January 2023. A month or 2 after the bills was paid I started receiving sms's from NUDEBT saying that my file has been handed over to them for debt collection. I emailed them my proof of payment and then didn't hear anything from them after that. Out the blue I am now receiving sms's saying that they will list me with ITC as I have money outstanding with them. No statements and no calls. I emailed them with all my proof but still I am receiving sms's saying that they will list me with ITC. No one is reply to my emails. Is there anyone that can assist me in dealing with this? Surely they cannot expect that I pay the collection fee if I paid my account even before my file was handed over to NuDebt??