Settled Account in 2019 but still receiving CALLS!?!

In June 2019 I was advised by these individuals that my Sportscene(Forschini Group Ltd) account was handed over to them due to an outstanding amount. I settled the amount immediately and received a settlement letter, which I then also forwarded to Forschini. I still continued to receive calls claiming that my account was owing. After numerous calls and escalations, they found out that the account with them had been “duplicated”. It’s now July of 2020 and this issue still has not been resolved. I’m still being told that my account is in arrears and that no payments were made. Honestly need to take this further!