FNB Loan already PAID UP

I have paid up my loan that I had with FNB though DMC. I received a paid up letter. To my surprise when I check on my FNB loan account, only 2k was paid towards my loan. Well i didn't take it serious as the issue is now between DMC and FNB. Come month end of April, FNB debited my account for the same loan that I have paid up through DMC. How is that DMC did not tell FNB that the account is fully paid? Why did DMC only paid 2k towards my FNB account? I need this to be resolved ASAP. I can't be debited for the loan that has already been paid up. Contact me on ***, my ID number: ***