There is no international toll-free number for T-Mobile.  Their toll-free numbers are only accessible from within the US because the company pays for every call that comes into those numbers.  The number to call from an international location is, 1-505-998-3793.  Contact Us (t-mobile.com)

Any number cancelled goes into being reissued after a couple of months.  There is never a guarantee you can get your number back and numbers cancelled don’t get any special treatment to their former assignee.  You will also need a new SIM because once a service is cancelled, that SIM card is no longer usable for any service.