Is it possible to secure Instagram?

Hey people, thanks for reading this. I hope I will find solution for my problem. Few days ago I "bought" Instagram account. I sent money via PayPal to seller. He sent me credentials, of course Instagram and Og Email. I told him to remove his phone and email from Gmail and from Instagram before I try to log in. I logged into Gmail, I went into Security and changed first password, then added my recovery email and phone number. When did this 3 changes it needed me code from his number that he removed from Gmail. Then I logged into Instagram, changed password, added my fresh gmail and verified it, also added and my phone number. I deleted Instagram emails from Inbox ( That say email changed ... ) because of security, emails with recover links ( valid for 15 days I think ). I thought this is everything I need to do but no, when I woke up I was logged out from Instagram. When tried to reset Instagram password it sent reset link to some mail I see for first time. There was no email from Instagram that say email changed on my fresh gmail or on Og mail. I couldn't do anything. Do you know what should I do more to Secure this Instagram. Also I had one bad situation few weeks ago, I was scammed by fake middleman, he took my account and I couldn't recover it so it looks like it is possible to secure gmail and instagram but I don't know how. That Instagram he stole from me, when I tried to reset password on instagram it needed code from og mail, I gave it to "middleman" too. When tried to click Forgot password on Gmail it said like We don't recognize this device ( I was logged in for 3 weeks I think ). It was impossible to recover. I tried on few devices same thing, Gmail doesn't recognize device. Can someone explain this? I will probably win Dispute but this waste my time
Thank you!