Bayfield Storage & Office Supply

I rented a storage unit from these folks on automatic payment. I was in the process of moving so my unit was empty from 7/28-8/17. I arrived to put my things in my unit that I have been being charged for and there was a lock on the door! When I spoke to staff they said because the unit was empty they rented it to someone else even though I had been charged for the month and had not been refunded my money! So they double rented my unit without a phone call or a refund. They say they will be mailing me a check... How is this good business?