Cancelling subscription

Hola,

I was a Tmobile customer in the US but left the country. I believe I had cancelled my contract but I've just received a notice for outstanding payment. Unfortunately I can't log into my account because it asks for my US number, which I no longer use and don't have the sim card to. Therefore, it seems like a catch22 not being able to tell them I had cancelled ages ago. There also seems no email address to send this notification to. They will be able to see there has not been any activity on the account for months.

How do I notify Tmobile that I have already cancelled to stop them chasing me for payment (without logging in to the account).

Thanks in advance,

Graham