Changing Gamer tags to a name that is taken but is inactive.

Sorry, but support gave you incorrect information. If the system says a tag is taken, then there is no way to get that tag. The tag system is in use on other Microsoft services, so even if it's not being used on a console, it could be in use elsewhere. Also,
the system doesn't see things like spaces as making a tag unique. So if you look up "gamertag" it may not come up right away, but still be shown as in use if it's written as "gamer tag".

Sorry but you have been given the wrong info.You cannot request for a gamertag to be freed up.

Gamertags are used on other services,not just xbox live so if it says the tag is unavailable then there's nothing you can do,you will need to choose another gamertag.

Do a name change on it, your account was probably inactive for long enough that microsoft retired the tag, all you have to do is do a name change, assuming the name isn't already taken again, and as always, the first name change is free

Hello there oOI BUMBUM IOo When an Xbox live member chooses an Xbox gamer-tag, they have the full rights to keep that gamer-tag even know if they have been inactive for years along with no gamer-score & no gold membership,
you will not be able to request for the gamer-tag to be forced changed. The owner of the gamer-tag must change it himself or when a forced gamer tag change is imposed due to the gamer-tag violated the code of conduct in any sort of way, if the gamer tag you
enter is already taken, you are prompted to try another gamer tag Also try to remember that gamer-tags are also tied to services like Zune or games for windows live. If a gt doesn't exist on Xbox or has already been taken, it might be in use on one of those
Additional services like gfwl.

Hello there Plumpy Platypus When an Xbox live member chooses an Xbox gamer-tag, they have the full rights to keep that gamer-tag even know if they have been inactive for years along with no gamer-score & no gold membership, you will not
be able to request for the gamer-tag to be forced changed. The owner of the gamer-tag must change it himself or when a forced gamer tag change is imposed due to the gamer-tag violated the code of conduct in any sort of way, if the gamer tag you enter is already
taken, you are prompted to try another gamer tag Also try to remember that gamer-tags are also tied to services like Zune or games for windows live. If a gt doesn't exist on Xbox or has already been taken, it might be in use on one of those Additional services
like gfwl.

The short short short version, No. As previously stated, you are prompted to try another gamer tag.
Sorry, ^_^