Gmail account used to register on Instagram has deleted!

I have changed my Instagram account's email address and now it is asking for confirmation of ownership when I trying to log in. They send security code for the first email used to register. But when I trying to log into that email, Google says that there is no account for that username. I don't know what happened to my Gmail account. I cannot sign up for a new account using that username. Gmail sign up form showing that the username already was taken. But when I going to sign in Gmail says…

Gmail account used to register on Instagram has deleted!