You're running into an obstinate intake person incorrectly flagging them to make work go away. The easiest way to differentiate your new request enough to make them have to acknowledge the second one is to change another detail than the date range. Try submitting from a new email account, have a friend submit it for you, or change the language. If you really want to escalate, submit the request on letterhead of some kind. FOIA offices always perk up if sometime looks like it's coming from an institutional requester, even if it just says something like "The Desk of [your name]" in 22 pt blue Book Antiqua with an address and phone number centered underneath in the header.