If you were from Teal and you made that character before the merge, your teal character still exists. When the servers merged a green copy of your character was made and you deleted that copy. Even though teal is gone all its names are in a database that is still live.
I had the same issue. At this time according to galach they cant get your name back, but once they wipe out the teal names it will be freed up. I put an x on the name I want in hopes its fixed soon and ill petition for them to pop the X off
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But they might not clear that database soon. I'm hoping it is, but it might be left alone until the end of green since the problem only effected so few of us and keeping the data doesn't hurt them much I'm sure data wise