My rights are being ignored ?

I had an account with RCS that was fully paid up on 10/09/2020 and I have a paid up letter with me. I was informed that it would take at most 2 months to remove the debt from credit bureau. It's almost a year later but my credit report still indicates that account as active and that the debt is not paid up, I've been running after RCS but I'm tired now, my rights are being ignored and I'm just exploring options of how can I best make them pay for this (Legally)