Credit card dispute won't work and can hurt downstream. What US did is poor CS, but it's not wrong under the t&c. They are entitled to collect the fare difference and you could have cancelled at the airport and not flown. In a chargeback, you will lose. Put simply, poor CS doesn't translate into a legal right to a refund of the $108.

Worse is that there are other threads here about individuals who have sought baseless chargebacks, running into problems with the CC issuer. Chargeback investigations are costly and time-consuming to the issuer and they'd rather lose a customer who puts them through too many of them.

Save the chargebacks for something really big or where you have a right to the credit.