I received an answer from their support:
That doesn't help us much....
I love answers like that. A typical support response to delay the case as long as possible.
If you read the article that came in the answer, it sounds like only the hashrate was really taken over:
Post the hashrate acquisition, NovaBlock will continue to operate independently, Poolin vice president Alejandro De La Torre told The Block. Other aspects of its business will also remain unaffected, he said.
For me this actually means that existing credits have not been migrated and should still be with Novablock.
However, I see not much chances in that: the Twitter account has been dead since the end of 2020 and
the official page has not been available for a long time.