U-Hall store manager never return my calls when they made a mistake in my account Philadelphia, Pennsylvania

U-hall made a mistake on my monthly storage rental bill. I phoned the property but was told that "they indeed overcharge me but they cannot reimburse it without the permission of the manager". I actually called three times and got the same message and the manager was consistnatly not available (despite the time I reached them). They took my phone number and said that the manager will return my call but the manager never did. I complain to 1800 UHALL  custer service and was told the same story - took my number and promise to call me back but they never did.