Hotels love slipping extra fees and charges to bills on checkout, hoping customers will not notice or if they do, be in too much of a hurry to fight for long. Disobliging hotel staff know they can wait a lot longer than customers, so often stonewall.
The Travel Insider, in one of their classic, massive series proposes a solution. Part 4 Hidden Extra Fees and How to Resolve Them in the section titled Giving in Without Giving In suggests:
If you’re getting nowhere arguing about the claim while checking out and you need to hurry to make a flight or business meeting (and this is what the hotel hopes, of course – they hope that the time pressures acting on you will cause you to give in), go ahead and pay them the amount they’re asking for, but write alongside your signature on the credit card charge form ‘Under Protest’ or ‘Disputed’. That way you can continue the argument through your credit card company, through the booking agency that made your hotel booking for you, and you can also complain to the Attorney General in the state the hotel is located in, if you feel strongly enough about the matter.
This is so simple that The Rapid Traveler is embarrassed to have not previously known it. The article recommends a similar approach to unresolved issues caught on check-in.
The full five-part series, How to Negotiate the Best Hotel Room Rate, has a wealth of information. Hotels are so varied and complex that there are no universal tricks. Therefore the series focuses on understanding the variables at play to be equipped to analyze specific bookings.