I work in a call centre (well, technically I now work from home ;) ) and I can tell you and anyone else who suggests this that it's the worst possible option. It doesn't cancel any contract (with anyone) and they are quite within their rights to charge you for the full length of the remaining contract in one go. The present situation may affect how they respond but generally it will be passed to debt collection. They're going to be busy due to the situation but just be patient.
That's exactly what they DON'T want people to do as it just creates more work for them.
Edit: And no, I don't work for Sky.