Did you activate when you installed the media centre pack, if so you are still activated. M/S are not spamming you they are simply making sure that you activate the media centre pack before 31st Jan, as the key code you have wont activate after that date. (it will reactivate after that date if you have activated already, in case of reinstallation etc.)
The reason for this is that media centre was given to you for free, after Jan 31st it will cost £10 or there abouts.
To check if you are activated simply use the charms bar (win key + c)click settings then PC Info it will show you if you are activated.