[Reubend]

I would certainly leave again - I'm really surprised that this happened to you twice, but any reasonable company would respect your wishes rather than forcing you into a role you never asked to do. It doesn't sound like you did anything wrong based on your description of the events.

[reluctantly]

I was kind of amazed when it had happened again, I was less experienced the first time. The second time with new company I was abundantly clear from day 1.

[yuppie_scum]

Fool me once, shame on you, fool me twice..

[hiptobecubic]

... can't get fooled again?

The answer, as always, is to tell them what you want and walk if you care enough about getting it that you'd rather work elsewhere than stay without it.

[drc500free]

Would they have fired you if you said no?

[reluctantly]

I don't know, but probably not immediately at least given the situation of not having a manager. If I was fully prepared to quit/be fired in response, I wouldn't be asking HN for advice, because quitting is obviously one option to exit the role.