From the additional info I read, it sounds more like the traffic wasn't the main issue.
Gambling is forbidden in a lot of countries or heavily regulated. Cloudflare uses a common IP pool for all customers, so a casino customer would possibly get their IPs blacklisted (by various ISPs). The Enterprise tier of Cloudflare has "Bring your own IP (ByoIP)", which they probably wanted to force onto this problematic customer to protect their business.
So it's actually a problem, not just them paying not enough (which is another reason to get rid of them as fast as possible).