MBD Attorneys

I had paid up my Woolworths loan account through MBD Attorneys as I've been doing each and every month. I then requested a paid up letter and I was promised that I will receive it soon and I waited and nothing was sent and I went checking my credit profile with a credit bureau and found that I'm again owing R91 on the very same account. The outstanding balance was R4976 which was also confirmed by MBD and I then paid it on time and had thought the account would be closed but instead they later added a R91 that themselves cannot explain. I'm starting to doubt business ethics of MBD Attorneys.