Wouldn't see that as a wits end scenario. Sky only guarantee hardware for 1 year then it's yours and your responsibility to maintain the equipment. As for sky pairing the device to card in my experience its normally up to 4hrs.
You brought a box off of Gumtree and it don't work! Give it back to the bloke you brought it from and put the tenner towards the new box sky are going to charge you for.
Oh and welcome to cf
