Thanks for reachin gout, I hope by now you have been able to get this resolved! There are a number of things that could be going on. You are indeed correct if you are on a Pay As You Go or other prepaid style pan, there definitely is no SSN association.
Is this a new account for you? Has the SIM card already been activated? Are you on a no credit check family plan of some sort? Asking primarily because it sounds like two lines are linked per the suggestion of logging in as PAH, but if it's a stand alone account or an unlinked prepaid plan, that opens us to some other questions.
Happy Friday, magenta2743739!
We want to make sure your new watch is working as it should be. Have you had a chance to read over Lauren's response? Also, did you purchase this from T-Mobile or somewhere else? From the sounds of it, your plan doesn't qualify to have the watch added as a cellular line; it requires a postpaid plan. Since you're on a prepaid plan, your watch will still pair with your phone via Bluetooth.
Howdy, magenta2743739! Apologies for the blast of emails from our Support Community, but we just wanted to check in and see if you were able to get this situation with your watch sorted out. Please let us know if you still have questions!