Release date is still TBC
The email you got from amazon was just an auto generated estimated January delivery date based on placeholder release date of December 31
Ignore the December 31 date as it's just the usual last day in december placeholder date that some retailers often use.
HMV don't have date listed and 88 Films don't have it listed yet
Amazon and Zavvi at the moment are using a pladeholder date.
88 films will list on their website closer to the actual release date this is not unusual as they most times only list for pre order a few weeks before and sometimes not until release date itself.
The exception is the 88 films webstore exclusives sometimes they list a few months before release date.
When release date has actualy decided by 88 films Amazon/Zavvi/HMV will then update their listings.