First step to take when someone is acting against the rules is to kick him.
If you are not a moderator, ask a full 18+ member (moderator or staff) to kick him for you. Get one on TS if necessary.

If he comes back in, and acts in accordance with the rules from that moment: good, no more action.
If he persists in his actions, have him kicked again (and again if necessary).

This normally solves 95% of the cases. The other 5 percent can either get a short or permaban, depending on the facts.

Apparently he has only been warned but not actually been kicked (that is not a strong signal........), and he has no way of knowing for sure you both are indeed representing OG.........

Therefore I think a ban is too much in this case.
Next time, please just get him kicked first.
His name is now connected to a report from you, which will count in future incidents with him.