As hc says you should rely upon the The Consumer Protection (distance selling) regulations 2000, study these regulations and if they are appropriate remind the supplier of their responsibilities.
They have a maximum of 30 days to deliver, if a delivery date is not provided, but it has and the 2 Nov was acceptable and the 7 Dec is not; cancel the contract in a permanent form under the DSR 2000, if they were found to be appropriate.