I wouldn't have told them to fuck off, but I'd have thought long and hard about the politics of the situation and what sort of edge I have (if my situation was as dire as yours was made to be). It seems like that could have been your moment.
You don't like politics, but it seems like at some point you have to come to terms with the necessity of politics to effect change in a situation, that is to say if it's worth it. You clearly have an opinion on how things should be done. Bottling that sort of stuff up is toxic.
I think in a healthy, functioning, company there is some politics. The thing about amazon is, it doesn't matter to anyone that I had pointed this out months ago. From my boss up to the person who reported to Bezos, every one of them would be embarrassed by it, but what could I do? Threaten to tell Jeff Bezos? He doesn't care. He was in the ticket and they were all pointing the finger at me. Me coming back and say "But, I pointed it out months ago"... would result in "therefore its your fault because you weren't persuasive enough!"
You can't make people take responsibility. Hell, Bezos would probably say I should have made the change anyway "You failed to take initiative". But if I had made the change, I would have been fired "You're not a team player".
Asscovering is the rule of the day and its very easy in that environment.
Making the code capable of the correct (but apparently not desired behavior), with a simple flag to turn it on is often the right solution (when you've received insurmountable push back, "Disagree and Commit!"). At that point, you document it in an oncall wiki and when someone finally decides it's actually a bug (or the people that said no 'go away'), it's sitting there with a good audit trail so you can tell your teams oncall one or two words and they can flip it over in a few minutes (after some QA). Note: I only learned this after surviving a really bad manager. I'm not saying you should have known to do it.
You don't like politics, but it seems like at some point you have to come to terms with the necessity of politics to effect change in a situation, that is to say if it's worth it. You clearly have an opinion on how things should be done. Bottling that sort of stuff up is toxic.
Anyway, glad you are out of that mess.