Xumo Box

While setting up my New Xumo Box it shows you are linked to account and now let us confirm by entering last 4 digits of my phone nember that is where I get stuck. It does NOT recognize my phone number which

I have been using for last 20 years for all my Xnifty devices and account. I tried to swap the Xumo box with New one but same thing. Xfinity assistant Chat were NOT of any Help.

I would appreciate if you can help