Yes it's probally against YouTube's ToS to get people to pay for content in unlisted videos, but the terms of service doesn't explicitly talk about using YouTube to host paid-for content - it is covered in a border statement though in their ToS [0]
But they should still at least be able to talk to a real human about it and get told the actual reason "Your account was terminated for commercial use of unlisted videos" instead of automated email bot responses/Or have been given some warning "This is against our ToS, your account will be terminated in 7 days"
[0] https://support.google.com/youtube/thread/38348285?hl=en
2. OP didn't say the videos contained ads. And why can't unlisted videos contain ads anyway?
3. YT weren't complaining about ads anyway. It was "cyberbullying" in one video.
It's most likely against ToS if you use said videos in a commercial way. Youtube isn't your companies private video hosting service.
> OP didn't say the videos contained ads.
No, but they were used to run their business. So it was commercial in nature.
> And why can't unlisted videos contain ads anyway?
Mostly a quirk of how Youtube works.
> And why can't unlisted videos contain ads anyway?
Looks like I was wrong about this one, sorry. It does seem like unlisted videos can indeed run ads. That being said, it still seems like a bad idea to run company crucial part of your business off of a free ad-based service.