My question involves landlord-tenant law in the State of: Florida

My Rental Office is charging me a late fee for nonpayment of rent between the 1st and 5th of this month. But I went online to pay it as usual and the balance due stated $0.00 and my bank information was no longer saved to my resident portal as to months prior. I called the office today on the 6th and they stated they are converting to a new web system. I asked if they sent out a notice, their response was No! Is this legal?