Can't activate cellular on my Apple watch 3, error message - Unable to Configure Cellular Plan

I tried to activate my Apple Watch 3 to my cellular plan, but it keeps giving me the same message over and over, "Unable to Configure Cellular Plan". Spent couple hours with Xfinity support and he had me reset both my watch and my phone, but the same error message keeps coming up. In my Xfinity account, it shows my Apple watch as one of my devices, but I'm stuck with the error message.