My Chevrolet app - unable to retrieve....

I am having the exact same issue for over a week now.  We have had the app for almost 10 years now with very little issue and the only thing I did in the past few weeks was change an email address.  Now the app won't work, I get the GMC sign in  page, I input my email and password and then I get the "cannot retrieve account details" with two options:  sign out or retry.  Neither do anything for me.  I called Onstar last week about this, it seems like a complete mess.  Our Onstar and GMC accounts are linked. A couple of days after calling it appeared the app was working again and then yesterday I went to start the truck from inside the grocery store and couldn't log in again.  I've uninstalled and reinstalled several times now.  My phone and all apps are up to date.  I think the Onstar agents gave up on me and closed my service/help order because it looked like it was working again.  But it's not and I can't really think what other things to do.  I almost feel like we need to delete all of our OnStar and GMC accounts and start all over.  All of this started with changing one email address because the old email account provider is ditching their email service.  HELP! Winter is coming and I want to be able to start my truck from inside a store or if I've left it in a parking lot somewhere.  Also the only reason we even have an OnStar subscription is to use this app.  If the app won't work then we don't need our subscription any longer.  Thanks!