@MontanaYeti - Mine initially did that as well. I once had the AT&T trial enabled so maybe that's why. I'm not 100% certain how I solved the problem.
First thing I did was I contacted "Mercedes me connect Support" within from the ME website and complained about the AT&T link.
(never heard back, but they may have fixed it ?? or maybe not
- see below...)
In the mean time - On my PC, I created a hotspotdrive account manually @
http://www.daimlerna.hotspotdrive.com/ - account only, would not add my van. (I think if the link was working correctly, it would have done this - also you may be able to do this directly from MBUX browser - see below...)
Then while poking around the MBUX browser, I found T-Mo hotspot drive being listed as a bookmark or something like that. When I clicked on it, it took me to
http://www.daimlerna.hotspotdrive.com/ - where I entered my hotspotdrive user name and PW - afterwards, hotspotdrive showed van now linked.
Sorry I cant give you a definitive step by step - I got mine working by pretty random poking around - but those are the two areas I think you need to focus on.
I would try the hotspotdrive website and MBUX browser route first - that may have fixed the AT&T link issue on its own.