I find this an interesting question - if you have a private repo with code in it and you get banned in this way can you export that repo? There could be situations arising where you don't have your code anymore because of the banning and that would probably be actionable.
Hopefully OP can recover any lost work(Or simply get unbanned), but I will venture a guess that buried in GH's TOS is something that amounts to "You agree to these rules, and if you violate them and get banned that is on you" and they can point at this/these clause/s and say, "Hey, OP broke the rules and that's that"
well then I would consider it might be worth talking to a lawyer, you have placed work into these repos, github no longer wants your business cool enough,
They don't have to provide you the service, that is totally their right - but it seems unlikely they would be allowed to keep your intellectual property at the point of service cancellation, especially given the reason for cancellation. They should provide a way to download the repos you want to keep for a reasonable time frame, if for example they send you an email
We no longer want your business, please get your stuff by this date or it will be deleted.
Then that would be one thing, but if they're saying
We no longer want your business, and you can never have your stuff back because that is our policy.
That's opening up a can of worms that their lawyers probably don't want opened either.
on edit: Were any of these repos paid for - then they really better solve it, even so they evidently derive benefit as a business for offering free repos so they should still provide a way to get your repo on service cancellation.
Finally they argue that reusing your code in training things like CoPilot is fair use - have your public repos been used in such a way and if so they are continuing to derive business benefit from your code while not allowing you access to it. Even bigger can of worms.
Considering the rather unfair cancellation (and basically any situation that relies on arguing you should have been more careful or you wouldn't have been taken advantage of is unfair) I think they should reach out, give you your code and say Good-day, sir (or madam, no offense meant).
But even if you were the person doing the starring of repos they would be in an iffy place to keep your intellectual property and not have a limited time, get your stuff back solution (which for all I know they have, I've never researched the matter)
Before you send that letter, talk to a lawyer. They have an army of lawyers. If you consider the account and its contents valuable, you should hire a professional who knows how to get the best results. DIY legal work is foolhardy.
