How do I unrecognize my device from an acct I no longer own?

So here's the situation: I am a Kpop fan. I was the creator of a fanpage about a Kpop idol on Instagram, but another person (let's say her name is Ben since I love Ben Afquack and her dad so much anyway) manages the account now.

It started out as my finsta account, but when the idol made their debut in the Kpop group, I decided to change this finsta to a fanpage and had to make another account for finsta several months afterwards (dumb decision I made, I know). I had this fanpage for around a year before I resigned from using the account earlier this year. I decided to resign from being owner of the account because posting videos was so stressful for me, and I was about to transition from high school to first year at college, which gives me even less time to manage a fanpage. However, I did not want this account to be put to waste and deleted, as it gained more than half a thousand followers unlike my main which has around two hundred, so I gave this account to Ben, who also manages Kpop fanpages as well.

When Ben logged in, her login attempt was marked as suspicious since she was from another country, so I had to approve her login. Afterwards, I logged out of the account. I then asked her to change the email and phone number of the account because it was not my account anymore. I also asked her to change the password of the account to something she can remember, as I was afraid Ben would not be able to regain access if she gets logged out of her account (also I did not want to have the key to accessing the account anymore, as the account is not mine anymore).

It has come to my attention that Instagram still recognizes this account as my own despite having a changed password, changed email, and changed phone number. I clearly cannot gain access to the account anymore. I do not know the password of the account, and there is no way in hell I can reset it, because the email and phone is changed. While most people just forget about the account they resign from being admin of, I do not, as I feel annoyed that I am still recognized as the owner of the account, especially since Instagram is developing technology which can potentially lead to my Kpop fanpage being banned just because my main account is banned.

Instagram used to be like where when you block one user, only that account gets blocked, then later it developed technology where if I block one account, the new accounts they make also get blocked. Now, Instagram has this new blocking feature where if I block two usernames a person owns, I check the blocking list and it shows up as one username, so if I unblock the username, both accounts are unblocked automatically. It seems like sooner or later, Instagram will develop technology where if my main account gets blocked, the Kpop fanpage I used to manage but gave to Ben will also be automatically banned (and my spam too), and I do not want one of Ben's accounts to be blocked just because I was blocked, because Ben did nothing to warrant that ban as she had nothing to do with what I would have done to be blocked. 

It seems like Instagram recognizes that account that clearly belongs to Ben now as my account. However, when I tested again on my spam account and blocked two usernames, one of Ben's other fanpages and my main account, both usernames show up when I check the blocking list. Seems that Instagram does not recognize Ben's account as mine because I never logged into her account, but one of her accounts is claimed by Instagram to be mine because I created that account and gave it to her. 

I was wondering if there is a possibility of removing my devices from device login history for the Kpop account that I used to have, as it is Ben's account now and not mine. I tried researching online for solutions, and people online always say checking login activity is the solution, but thats not the case because login activity only shows devices the account is logged into and not login history.