Blame the system, unwilling to help

Rented a storage unit and a parking space - was paid in full until end of August, found an apartment to move into on the 16th of July and fully vacated on the 17th of July. Was (wrongly) under the impression that I need to give a month's notice, so as I gave the notice on the 15th of July, I assumed I'd have to pay up to 15 August. No one mentioned that you can't vacate on the 15th without paying for the full month, and that I might as well just give notice to the end of the current month, as the unit was already empty. It's now the 20th of July, still ample time to find a replacement for the unit for the month of August - and happy for the credit to be app**** to the parking space rather than being paid back to me, but absolute unwillingness to assist a client and blaming the system for their helplessness.