cant login to my account

I purchased tmobile internet in August. The store setup my Gmail an my payments. Last month the payment was no longer valid not sure why. I can't update my cc info. It says my Gmail isn't recognized  yet I can login with it and it says enter phone number which I did off the router it sends me code verifying. Then says email not recognized. Been doing this for months. Please provide the email you used when purchasing your t mobile service. So it won't link the phone number to my account

 Even pay my bill does this.  It just keeps looping me around to enter my email address then phone number to link acc