Can landlord claim you owe monies from credits given to you?

When I switched apartments back in October the office personnel work out the fees to move with me. Because i require the office to do not updating (painting, carpet change,...) she waived some moving fees. In Jan I went into the office where she noticed I actually had some credits to my account. Excited, being just after Christmas spending, I wrote a rent check for less than the usual. Now, nearly 5 months later, the office has contacted me saying I owe $379. The old office person has been fired... apparently there was all kinds of issues with her performance. Giving a ledger of payments and debits makes no sense... even the current employees could not explain. Only to she she gave unauthorized credits. Can i be held responsible...it seems to me that she was an agent of the management and it is their problem not mine!