Much needed help involving xbox live and my rank

I’m new here to the forums, and so I hope I have placed this in the correct forum.
My brother and I have been playing XBOX: LIVE for over 2 weeks now, and have had a lot of fun.
Our only problem is that i’m a guest while he gets to play his real account.
I decided to use my Campaign account and use a few of the 2 free day XBOX: LIVE certificates received from various games. I renamed him, set up my account, and was ready to go.
The system had told me that I either 1.) forfeit all of my credits and restart as a Recruit, or 2.) Return as a “default spartan”.
Not knowing the difference, I chose to “Return as a default spartan”.
I’ve now played a couple of games with my bro and gained no rank whatsoever, I am unavailable to use a gamertag, and my rank icon remains a grey translucent gray. Also, if i’m offline, all of my armor, rank, colors, emblem, everything remains, but when I enter matchmaking, everything disappears.
Is there any way that I am able to reset this in order for me to gain credits and use my spartan’s real attributes. Thanks to anyone who can help