I believe that it's no longer possible to get names freed. I wrote Twitter support recently about releasing a name that was created over two years ago and used once to send a single nonsense tweet (twice in a row). It's never been used since.
The support person was very clear and wrote back quickly to say, and I'm paraphrasing, "We don't do that anymore." She added that they have some plan to reap unused accounts maybe ever somehow, but it was very vague. Vague enough that I'm not hopeful they will ever do it. (You will find a number of discussions online about various methods that used to work for getting a dead Twitter account released. It seems they got enough requests that it was more work than it was worth. That's my guess, frankly.)
If you have luck somehow, please write back to say how. It's really a shame since so so many names were taken and just lying there unused.