I am actually fighting something similar right now after moving out of an apartment and charging a bogus fee - take a look at MD Statue §8–203, specifically (g)(1) & (2) - https://mgaleg.maryland.gov/mgawebsite/Laws/StatuteText?article=grp&section=8-203

Depending on when and how they notified you of withholding (greater than 45 days), you may have an easy case in small claims court.

Good luck.