The wonderful French train company wouldn't refund the ticket either and instead insisted that we might use it one day on another trip to France. Thankfully by the time I got to the front of the line to chat in broken French to the ticket administrator, I had already accepted my fate after hearing a number of tourists (not Americans mind you) yell and stomp their feet uselessly in hopes of obtaining a refund.
[1] That was a fun adventure too. At CDG, well I found out later that taxis are "allowed" and are the same price as the Uber ride and so we could have avoided this by just taking a taxi through Uber, but a group of folks from Great Britain were ahead of me in line and I came across them later when looking for where to get a taxi/Uber. There were rideshare signs or something but they didn't lead anywhere that made sense. They seemed rather aspirational. Well, one of the members of the British group spoke good French (or good enough) and found out the secret spot to go after chatting with an airport employee I think it's at Terminal E (someone else may know for sure) or something and so my wife and I befriended the same British group and went along with them for the long walk over.
We were able to get a ride, though not cheap. Of course the bus was an option and we're no stranger, but we were on vacation and the $50 ride was just chalked up to the cost of doing business. We were already 2 hours behind schedule because of the train fiasco.
All that to say, I think using an American credit card these days is the least of your concerns. I was surprised to see American Express taken rather much more widely than anticipated. Be careful getting gas though as they place holds on your card for $250 or something like that, and once you get enough holds you can't get any more until the prior ones "roll off".