EDGARS RCS charging interest on a closed account more than 2 months later. they do not respond to queries.

I closed my Edgars account immediatly on receipt that the interest free accounts are no longer - this without any notice. So at Edgars N1 City we phone the RCS call centre and get settlement which cleared the account completely. After numerous e-mails to RCS to confirm, they now send an outstanding balance with interest. From all the RCS complaints, I think it is time to approach the National Credit Regulator. it seems I am not the only one that gets charged interest out of the blue. This should not be tolerated.