EXTREMELY ANNOYED!!!!!!!

I am disgusted by the service Cell C has given me. I had a contract with them from 2018, where after a while I couldn't pay and my debt was transferred to Shapiro Shaik DeFries and associates and I paid my debt there to my surprise my credit score was never updated. A few weeks back I recieved an email from Cell C telling me that my debt has been sold to Nimble Group attorneys. When I call Cell C they send me pillar to post. I even sent them proof of payment but they are ignoring my request. Now an enquiry has been made against my credit score. I honestly don't know of any way to deal with Cell C