My story with revolut is one day, without warning before, when I opened the app, I'd seen info to update it before I do anything with my money. And in Google Store there was no newer release for my version of Android. The only way to complain is to do this in-app so I was not able to do even this. Basically, I was cut off my money, completely.

After two days I found on their site a form to cancel my account. Which was still not easy, before this they tried to keep me as a customer (suggesting for example to buy newer phone :) )