That honestly seems loosely interpreted, since in this particular case it's not the impersonation or misrepresentation of an individual, but simply the shared use of multiple individuals, in which all involved parties have consented. While it could very well be considered a ToS violation, I doubt it was the trigger, even if it could be spun both ways.

If I had to guess, it's probably a case of the payment system's pre-programmed fraud detection giving a red flag due to multiple payment methods that don't correlate to the same individual and choosing to lock your account down in terms of future payments and subsequently alerting Nutaku in the process, which Nutaku is probably also programmed to follow suit. From then on, Nutaku's approach (from a dick-wad business perspective) would be that they could re-activate your account but there's no particular benefit in doing so since you still won't be able to make any more future purchases anyways so long as that payment portal's locked down.

And I know what you're gonna say, something along the lines of "just make it so that I can buy gold again, that simple". Yeah, it probably would be that simple if it weren't a separate-party system that deals with the payment side, and while Nutaku may be willing to re-activate the account, it's difficult to say if the payment site would do the same, more so if they have a list of confusing terms that your little multi-user stunt potentially violated.

And finally regarding your gri-...suggestions:

-General Note: Under the terms of use, Nutaku technically reserves the right to revoke your account access or even outright shut down the site for no reason whatsoever, even if you were a "law-abiding citizen" of sorts. While game sites almost never exercise that right, it's there to say "we can do what we want", so your "should"s don't exactly apply. That being said, I get that you mean "should" as in "this would be a much more hospitable approach to users" but even so...

1. Eliminating the consequences (in other words, not banning the account) is out of the question. Allowing suspicious activity to run free, especially in the perspective of fraud, is incredibly dangerous and runs the risk of stirring up further problems down the road if not stopped early. I'm pretty sure the payment portal would prefer that they stopped payments to an account early and had to deal with a customer wanting to make more payments instead of having to deal with a non-customer who got his/her credit card(s) stolen and wants a massive refund in the time the payment site did nothing. The multi-payment warning sounds nice but ultimately you won't be able to see it since the site would automatically deny you access thereafter.

2. From a business perspective, importing existing account data into a new account is wasteful on time and available resource. Plus, other than bypassing it for that one instance, it fails to solve the underlying issue as your account will get locked down yet again if it senses the same suspicious activity from before. From a moral perspective, it teaches you, the user, absolutely nothing and gives you the impression that you got away with it scot-free and can just do it again expecting to get bailed out down the road.

On my own personal take, you seem to be talking in a way (or just lacking the tone that would suggest otherwise) that seems like you think (and will continue to think) having several users run your account is perfectly acceptable (I honestly don't know whether or not it is but I'd suggest you find that out one way or another). By inference, I'm thinking there's a possibility that during your time contacting customer service you came off to them as unapologetic and likely to create the same issues again, in which case naturally they'd refuse.

There are frankly quite a few things that I don't quite understand. Was it Nutaku or the billing portal that chose to lock the account down? If it was Nutaku, was it due to a specific ToS violation and are they expecting you to prove you won't do it again before they reconsider your access rights? On the other hand, if it was the billing portal, what would it take for the portal to reinstate you and subsequently allow account access?