New broadband router installed fine but cable to socket doesn't work

[JRDS]

Switched from BT broadband to Sky broadband - this happened earlier today. Sky instructions are fine and troubleshooting about cable connections are very clear. However the instructions didn't account for a defunct cable to phone socket. After an hour I tried using the original BT router cable and it worked and installed immediately. I am a happy new customer but would like to point this issue out to other new customers and Sky support team. I expect I am not alone in experiencing this. 

[Highlinder]

@JRDS  Which cable is that you are talking about? Are you able to post a image of it.

[JRDS]

It tells me that I don't have permission to upload images.

The Sky cable was supplied with the router - black cable with purple end plugs shown here: 

http://storage.sky.com/prod/helpcentre/manuals/skybroadband/sky-broadband-hub-setup-guide.pdf

BT sent me a pre-paid nevelope to send their router back which I did with the Sky cable (hence no photo) and I have kept the BT router/phone cable since it works.