Last time this occurred (Chelsea stealing a player) they agreed to pay Manchester United £12M to stop United complaining to FIFA about John Obi Mikel being lured to Chelsea and breaking an agreement.
They should have been banned from the transfer market then (2005).
Maybe they should have bunged Lens a few £M to shut them up. It would have been less costly than being stuck with a load of geriatric players for a couple of years.
Chelsea seem to consider the rules are merely guidelines. Chelsea aren't the first to have this punishment meted out to them - if memory serves, Roma have been punished in a like manner in the past (and a Swiss team as well???).
It beggars belief that Chelsea were bitching about Manchester City recently when Chelsea are by far the worst in the Prem for this sort of behaviour.
Perhaps this will force them to realise that they have to play by the rules.