We are only permitted one device change per calendar month I'm afraid.
By removing the device you had already registered this month, you are now out of luck. However, the good news it that you'll be able to add a new device on Friday (1st Jan).
Removing all the existing devices was the worst thing to do since, as you have now found, you can only add back one device each month.
You can try calling Sky and explaining the situation to them, but the chances of them overriding anything a pretty slim as the change restrictions are a condition of the licencing agreements.