Deposit rent not paid back

The supplier is refusing to pay my deposit rent claimiung that the are penalties that i only got to know about when i requested my deposit to be paid. this is despite the fact that I have given them one month notice prior to me leaving the place, when i left myself and the landlord were fully aligned that my account was uptodate. i cannot afford not to have my deposit rental not paid to me despite my account being uptodate when i left.