Rcs is no good

I paid up my account in December and I told them to cancel the account with Immediate effect, January I got an email for overdue monthly fees, I was in the process of applying for a bond and they black listed me. I quickly paid what ever they said was due and called them of which I was told I was incorrectly billed they then proceeded to send me two letters one saying I don't owe Rcs a cent and the other a letter of apology for incorrectly billing me. Just this week I received another statement showing that they are billing me for a collection letter. I now try and call and 20min later I'm still on hold.