Altramar II Mobile Park

I had received a letter from my landlord for a late fee of $60.00 and to pay before a certain time. Now im 100% positive I had turned in the money into the office before the due date. I am confused due to there being more than one notice but the landlord was going off the first one that was given. I want to know if I can get help and or more knowledge about what I can do about this because now my little boys and I have no home and are living on the streets. This is not right in any means. Please help me.