MBD failing to to address FNB account that I was paying through them

I had a Cheque account with FNB that was handed over to MBD Attorneys for collection. MBD called and offered a 20% discount and we agreed on 6 month payment plan of R5445. 00. I paid managed to pay off my account in 5 months. I've been calling MBD to arrange a paid-up letter to no avail. Today I received an SMS stating that the very same account has been handed over to Ramdup Attorneys for collection. I called FNB the whole of today, to ask why did they hand my account over to Ramdup Attorneys because the account was paid up with MBD, but with no luck. I even went to the branch but still they couldn't assist. I also called MBD Attorneys but they told they can't assist since the account is closed on their system. Please help