Xumo Setup PIN

To set up my xumo box and link it to my xfinity account it needs a pin. It does not accept the pin I would have used, it does not accept the last 4 of ANY of the phone numbers on my account. The name it displays is the one on my account. I've called the number it gave me and spoken to Xfinity Support who was convinced that the HDMI cable was somehow the problem with an ACCOUNT PIN. This is a common issue and so far Xfinity has been USELESS so far in resolving it. Constructive help is greatly appreciated.