ACCOUNT PAID UP AND IN CREDIT NOW ALL OF A SUDDEN OWING AGAIN

I have a complaint on MBD Attorneys, I received a notice that I have outstanding money on Jet / Edgars account. I then went ahead and paid all the money due on this account. I was in a credit and the idiots send me notices that I still need to pay the account. For being in a credit. Today I get an sms stating I owe them R153.44 after being in credit for 2 months the prior months. How is this even possible being an attorney firm? I even received the amount due to be paid from them directly.