You say you removed the Hulu app? That indicates the Hulu subscription is direct and not through Roku Pay. If you need to confirm that go to https://my.roku.com and click on Manage your subscriptions. Ensure there is no subscription there. I suspect there is not, but you should always verify each important data point.
If you are able to remove the Hulu app, do so. Then reboot the Roku. Then reinstall the Hulu app.
Did it autologin to that account again? If not, your issue should be solved and you can log in with your Hulu account.
If it did autologin, that means Single Sign On (SSO) is logging in before you can log in differently. So, you need to look at a few other things. Depending on what is found at various points, there could be a different set of things to try.
First, go back to https://my.roku.com and scroll all the way to the bottom. Do you know about each and every Roku listed there? Are all of yours there? Are only yours there? And can you verify the serial number on the Roku with the Hulu issue shows up in that list? (Settings > System > About)
Roku Community Streaming Expert
Note: I am not a Roku employee.
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