Part of the problem I am having is finding notice that the trip is "officially" cancelled. When I reached out to Eurostar, they just said "it's not cancelled yet", even though they aren't servicing the station and clearly aren't going to be anytime soon. As best I can tell, the only way I will be able to find any "proof" is wait until the day of and take a screenshot of the train status page.

I am planning to try with Eurostar one more time once the travel date hits. If that doesn't work I will explore the chargeback route, but I worry that won't work because I purchased the tickets a long time ago.