Edgards account trouble

So I had an account with them around the time when Nimble bought them over, after that I pad my account in full which was R2800 and got a letter stating that I have paid it. This went on to be clearscore record that I owed both Edgars and Nimble R2800, after a while Nimble went away but Edgars stayed and is currently still showing I owe them money, after I have called them and Nimble for the last year and a half trying to get it off my record as this is effecting my credit score badly and I cant get any lone or even a phone contract for that matter.

If anyone can help me with advice on how to sort this out asap I would appreciate it a lot, like I said I have the proof that my account is paid in full. I'm young and for this to be affecting me in this way is unfair towards me and my future. any advice would really be appreciated thank you in advance.