Patience is key. It can sometimes take a long time to get prizes. It can sometimes come very quickly. Sometimes information is forwarded, soemtimes they contact you for the shipping address. Also, did december give you an option to pick seeds or was it a predetermined set of packs? That would obviously need some direct contact if you need to make choices. They should* contact you, but if it's mid february and you haven't been contacted, send a DM to the 'official' rep if ther is one. If not, send a dm to growdiaries.
Speaking with others that also won that month can help give you a heads up, too. You can let each other know to make sure nobody is left behind.
I've never been involved in a contest where the prizes were not given out, but I believe it has happened before.
Just remember, you catch a lot more flies with honey. It's free stuff. Be polite about it, but don't let them forget, if it's been ages without contact, lol. Act an ass to whomever fills the orders and maybe they deal with you last... maybe after a 2-week vacation and not on a monday or tuesday for shits and grins when they get back, lol...