Gamertag ShadowKiller

Had a quick look & that gamertag is taken.

Someone has the tag Shadow Killer & as the system doesn't recognise spaces Shadow Killer is seen as the same as ShadowKiller.

Sometimes people also claim a Microsoft Gamertag, yet never play on Xbox. They may claim a name and then only use it on W10, for example, or for other Microsoft products. Sometimes this may be the case if you can't claim it, but don't see it being used.
The other option would be that part of the GT is not allowed, like maybe the word "Killer"? Although I'm not sure if that word has been banned to use in the GT system or not.

When you check to see if it is available what happens?

Also keep in mind when you check at account.xbox.com and do a search to see if its available the system does not recognize spaces or capitalization so you would have to type in the gamertag EXACTLY as the person did when they originally set it up if do not
it will act like the gamer tag is available but it may be taken with a different spelling.

I will give you some examples

The system sees all of the following gamertags as the same.

ShadowKiller

SHADOWKILLER

shadowkiller

s h a d o w k I l l e r

with that long of a gamertag there could be about a million different ways for someone to of put the gamertag in when setting it up.

Hey there Shadowkiller!

Before we get started, could I have you provide a bit more information so that people trying to assist you can have a better understanding of your situation.

Please read:
forums.xbox.com/.../1621667.aspx And post back in full detail (scroll down for the questions in bold).

Thanks!

Hey Shadowkiller! Just so you know, the Xbox has 7 ports to be forwarded, but you mentioned Call of Duty and Destiny both say moderate - this is actually because Activision games all have specific ports that have to be forwarded JUST for them, which is really
annoying! Are those the specific games you mention are disconnecting you in your first post? If so, try this:

For call of duty, add UDP ports 3075 and 3076 to your port forwarding, and for Destiny, add 1001 and 1200, also on UDP.

Oh, and don't always trust when a website tells you your NAT is closed, I've never been able to find a good desktop app or website that accurately reflects my NAT. The best places to check are by doing a Network Test in your Xbox One Network Settings, and
by looking at the multiplayer menu in the game itself (I know CoD multiplayer lists the type of NAT you have. I don't think Destiny does, iirc, but if you forward the two I listed, you'll be good to go.)