I am sorry to inform you that we are not actually 343i. We are merely a fansite
You can contact 343i directly here: https://www.halowaypoint.com/en-us
Although I do not believe 343i will provide you with a download of the game. I have never heard of them doing so in the past, and I think you might have to end up returning the disc because it is scratched.
I'll do my best to help anyways. Here are some things you can try.
Clean the disc(if you don't know how just google search) and then try to see if it works then.
If not then clean the disc again and try to install the game into your harddrive(when the game prompt appears just click the "Y" button for details and click "Install to harddrive"
Also what error message are you getting when you try to play Halo 4? Are you using Disc 1 and not Disc 2? Have you installed all the contents for Disc 2 yet?