The "utility" company guy finally got back to me this morning at *looks at phone log* 6:44am. I was sort of up. I was doing my usual "wake up, be too tired to wake up, fall back asleep, repeat" cycle (I need to find my sleep pills, then find a day to use them). Anyway, there was some confusion as to what the issue actually was, but once we got that sorted out he agreed the bill was definitely too high, would contact some other department about the final water usage, and contact me back. He called back only a few minutes later explaining they had paperwork which said I didn't turn the keys in until the 5th of June, signed by the assistant manager, even though the lease was up the 3rd of June and the keys were actually turned in on the 11th. I would need to contact the apartment community and get them to call him to change that.
I immediately called the apartment community, spoke with the assistant manager, and once again got in a verbal debate regarding just how much I'm supposed to be responsible for. He kept saying that I was legally bound to pay for the rent and utilities to the end of the lease date regardless of when the keys were turned in, despite what the utility company guy said and despite the logic that you shouldn't be charged for usage during a period you weren't even in the apartment. He even tried asking me if I had paperwork confirming when the keys were turned in, but I told him they had all that paperwork. I think he finally got the point that I wasn't going anywhere until they changed their mind, so he said he would call the utility guy up right then and explain the move out date, and would take my word on telling them the keys were turned in on the 11th. I think he finally did the math on how much of their time, and thus money, I was causing them to waste by contacting them.
A few minutes later the utility guy called back saying the assistant manager had confirmed everything, that the two daily rate items would be refunded for the 22 unused days, and they would get a credit appended to the account and additional refund check mailed out. He would also email me a receipt with the new bill rate and what-not as proof of everything that has been discussed (I have yet to get that, but figure it'll take some time to run the paperwork and print out a new bill. I'll give them a couple of days).
No one wanted to give a reason why the daily rate was used instead of metered rate during the last month, but at least this was progress. For lowering the final bill by almost half, and not having to deal with this anymore, I'll take it.