Claiming an instagram/twitter name that is currently not being used

I want to have an instagram and a twitter account as an author, because I will publish a book soon. However, the name I want to use is not available, but the persons holding that name have not been active on these accounts for years (10 years already). Therefore, I would like to claim these account handles (@) to be able to use them as an author. If you are sure that you know how to do that and would like to take the job, please contact me and I'll tell you what name I want to claim.