You can only raise you channel package or add premium channels or the few channels like dog TV online, you have to call to remove the premium channels or lower your package.

The email headers look legit to me.  It did take me to the channel-opt-in page, where I was able to authenticate, but when I tried to submit the form it always generated an error:

Yes, that email looks legit. Have you tried going to this website? https://signin.att.com/dynamic/iamLRR/LrrController?IAM_OP=login&appName=m45917&loginSuccessURL=https%3A%2F%2Foidc.idp.clogin.att.com%2Fmga%2Fsps%2Foauth%2Foauth20%2Fauthorize%3Fresponse_type%3Did_token%26client_id%3Dm45917%26scope%3Dopenid%26response_mode%3Dform_post%26state%3DHALODTV%26nonce%3Dsdfdds8%26redirect_uri%3Dhttps%3A%2F%2Fwww.directv.com%2Fmsapi%2Fdtvloginms%2Fv1%2Fauthenticate%3FnextUrl%3Doverview

When you put your email and password into the required area, click "Sign in". Once redirected to the DIRECTV profile, hover your cursor over "My Account" at the top right, My Programming (submenu popup), and click "Change Package." Now select your new appropriate package selection by clicking "Change Package." A pop-up will appear to confirm your choice. IF you get a black bubble when trying to click "Change Package" (says to call 800-531-5000) then you must call DIRECTV to change your programming package. Their number is 1(800)-531-5000.