If it were the email address, that would be easy to get around as you can create as many email addresses as you wish, I have several for different purposes.
If it is the Ip address of the router, this would be more difficult, but of you were away from home your Ip address would change, so you could create an new ID without being spotted, but as soon as you returned home it would flag up the banned ip address. But you could have more than one legitimate user on the same router. The specific computer could be tracked via it's MAC address, but a user could get round that by using their phone or another computer.
I suspect they use Ip address, this is what most forums and game site use. Game site require anyone using the same ip address as another to notify them first.