Unwanted forwarding of emails to my phone

So, I set up automatic forwarding from my email to my phone. It didn't work and now I want to cancel the forwarding. There are two parts to this problem.

1) I did the forwarding process correctly -- In my gmail settings, I set up all emails to automatically forward to 10digitphone#@txt.att.net, and I confirmed the forwarding via a link that was texted to my phone. But the emails never even forwarded at all. Now I get an email error message, and my inbox is stacked full of them

2) Since the "email address" of 10digitphone#@txt.att.net isn't a real email address, I can't go into the settings and turn off forwarding -- when setting up auto forwarding from email to email, you have to confirm forwarding on both emails in the settings. And clearly, the problem is that I don't have a settings to confirm or change it. 

So how can I sign in to my @txt.att.net email, or how can I turn off auto forwarding from my phone?