Can you take a screenshot of the avastUI > Settings > Registration, like the one I posted and attach it.
This will show if you are already registered, because if you aren’t there should be a different screen to the one I posted to allow for the manual input of the free version registration.

Having posted your key twice, it can be harvested and that could well end up being used by many others. This in itself could result in it being blocked by avast leaving you blocked also.

Also did you try what I said, ensure there are no trailing spaces when trying to enter the registration key ?