[zegerjan]

The reason you couldn't delete the blob, is because someone forked your repository and GitHub uses git alternates for deduplication of fork networks.

I think you could ask GitHub if you can recreate your repository without the offending blob, and you should be good again.

[aliostad]

This is essentially what I did using bfg tool. They still took it down.

https://help.github.com/en/github/authenticating-to-github/r...

[zegerjan]

I'm saying the blob was in a new repository, you had no control over. You couldn't have removed it, you could only make sure it doesn't get referenced in _your_ repository. Which is what you did.