Nine Mile Road Self Storage

We have had a storage unit with the company "nine mile storage" in Richmond, VA. last month we paid on the 5th online (it would have been a late payment if paid after the 6th). My husband received confirmation in the form of an email receipt (almost immediately) that states the date we paid, and how much. We then received a letter in the mail saying we owed our normal fee for the month coming up plus a 165 dollar late fee for "being late" the previous month. My husband immediately e-mailed them and even though he told them of our receipt from their very own company he was told two different times that it was because their system didnt register the payment on time. But it was THEIR system that sent us the e-mail which means logically you would make the conclusion that their system received the payment in order to send out a receipt, right?! I am beyond livid right now, we just have been through a lot financially and this is a set back that should never have happened and SHOULD BE FIXED.