Then this is an issue for BT to investigate and fix, however, they will not accept any fault reported by customers regarding broadband, it will have to go through SKY...

Contact tier 1, advise them of the issue, ASK to be put through to tier 2, who ( Normally ) Know what to do for faults such as this..

Basically there is crossed wires somewhere, where, lord knows..!

Tier 2 will have to notify BT of this, who will in turn run tests to establish where these crossed wires are, they may be in your socket, may be at your exchange, once it has been identified ( normally takes 48 hours for BT to find this ) then they will notify SKY of the ETA for the issue to be resolved, or that an engineer will be required to visit your premesis!
Best thing to do is to Call back into tier 2 after 48 hours to try and push them on a but quicker, there is 100,000 customer ring into SKY each month with issues from, forgetting to turn router on, to serious issues such as the above.
So try and understand that there is very little tier 2 can do apart from WAIT on BT.