Depending on where you live, landlords will sometimes ask for "First and Last month's rent" on the first day, in addition to the security deposit. It's illegal where I am, but apparently some people will ask for that.

Where I live, you would have paid $250 for your first "month" in addition to the $600 security deposit when you received the keys. The next full month would be due on March 1.

Like the other guy said - ask him for a break down, that indicates what the money you gave him was actually for.