They make it appear as though the usable funds are higher than they actually are. They do not show "Available Funds".
The FDIC is involved now. The letters are sealed and will be sent by certified mail Tuesday morning.
You should not have to call your bank to take their hand out of the cookie jar - esp. if the obvious, printable transaction history shows the account never going negative during the overdraft period.
They sound despicable. I hope you're looking for another bank, even as you follow this through. May the New Year bring you happier tidings!