landlord of commercial real esate making unwarranted deductions from security deposit

we were given 30-day notice for a month-by-month lease of a commercial building, but we notified the landlord that we were going to move out by end of the month instead of at the end of the 30-day notice (which includes 9 days of the following month). met with the office manager for a walk-through on the last day of the month and returned the premises. did not receive deposit within 30 days after moving out, contacted the landlord but they claimed the office manager we met with had quit and they had no way of contacting him. landlord is trying to deduct rent for the extra 9 days after our move-out date even though a new tenant assumed the space and started renovations within that time period. unfortunately we didnt get written agreement that we would be ending our lease at end of the month