Well, saying that gmail is very hard to get in with a brand new ip is true, and changing recvoery options is even more diffucult is also true unless you login only behind vpn from different locations, in that case, with the password or the right recovery options, it's fairly easy to get into a gmail account and take the ownership.
Sadly, if you're password is no longer working, and recovery options have changed, forget about taking it back.
Your best move is to ask the new owner to send any data you might wanna recover (pics on drive or files) but there's litle chance they do it.
Also, I'd check every account linked to that gmail account, especially those with which you have money or cards tied to them (hosting, e-commerce, paypal, etc..)