So i got HALO MC on release date and i heard i was suppose to get HALO Odst for free or something and it says i have to buy it?
Taking a quick look at your service record, your first achievements weren’t unlocked until April. To be eligible for ODST you needed to have played while connected to Xbox Live before December 19th of last year. If you’re positive you meet that, check out the MCC FAQ link in my signature. All the details about ODST and how to claim it are there 
Your lucky