My gamertag isn't allowed?

Like someone else said wait a bit for the server to recognize the names not in use anymore

It's likely that the old gamertag hasn't been released yet. I would recommend you contact
Official Support
to see if they can assist further. It's an automated system and so it's possible that even though your tag has changed that you can see, the old one hasn't been released yet to allow it to be claimed again. It's not guaranteed that Official Support will
be able to help, but it's that or give it some time.

Hello, I've read your post, and I believe I understand your position. The Xbox Ambassadors are here to help.

I noticed you said you changed it, and then immediately attempted to change it right back. Please be advised that it takes 24 to 48 hours for changes to occur, and also only one change is free, then you have to pay for a change. Below I have included a link
that you can copy and paste into a web browser to follow-up on this topic.

https://beta.support.xbox.com/help/account-profile/profile/change-xbox-live-gamertag

one off my friend’s has this problem too. we waited a day & he was able to claim it again, wait 24 hrs since unchanged and it should work

Far as I know nothing is wrong with "Huskie" far as i know its just an alternative name for a husky and possibly someones name but other than that i dont see anything wrong under the guidelines. Just give it some time I'm sure it will be fine. It's not
unique so maybe they are putting a crazy number on it like Huskie109 etc? Who knows. Just doing a bit of research there a a few names with the exact spelling and a few variances so maybe they are trying to give you a number like i mentioned before.