Return old gamertag

Have you tried checking
here? I used it to check two of my old gamertags, and it allowed me to change it (Example
here). Even if someone is using the gamertag, you should be able to use it (The only difference is you'll be given a discriminator at the end of your name, example of this would be
here). Now if your GT is over 12 characters long, just press the customize button and you can change it to whatever you want it to be as it's apart of the old GT system (Example of
this is my GT that'll appear on apps and on console is Madam Sukii, but in game, it'll appear as ).

Did you check with that link I gave you (The first one)? Because if you search up your current gamertag in there, it should give you
this prompt. If it's doing that, even through your gamertag isn't that, you should probably talk to Xbox support
here.

The price is not the issue, its my old gamertag, its saying choose a different one, but the tag i am trying to retrieve is not active.

My gamertag use to be original and it is only 5 letters, but tells me to choose something else

Hello! The only way to change your gamertag is paying $9.99 for the change (You should have a free offer to change it unless you've already used it).