I’ve been in chat with support for we’ll over 2 hours this week and was told too post here by them on how to get my 1 month of gold for the halo MCC since I never got the code for it while everyone else did.
This would be better placed in the support forums, but I can help you out here.
> Have you recieved the nameplates and avatars? If you have, the free month should be dropping anytime and you will get ODST. If not, I would pass a message over to B is for Bravo and he can check with the team for you. It may also be possible that you have the free month already, you just didn’t get a message. If you go to https://commerce.microsoft.com/PaymentHub/Subscription and then click on the ‘view history’ link under Xbox Live Gold - It should look something like this. From there you should be able to tell from the dates if you have the free month or not. My account was updated a few days before I recieved any messages. Hope this helps 
Iif you have twitter, you can also send Bravo a tweet if you need to contact him
Good afternoon,
I was one of the lucky ones to receive 1 month free xbox live gold, I get an email with the code, however, I see messages in my inbox (where I had saved code) was removed, I complained on xbox and they say to put my complaint in this place, that I must make 343 Industries?
If you make a post over on this support forum, someone over there will be able to help you out That is the forum that Xbox Support should have referred you to