I'm logged into the scammer's account and can't log out

Your only option is to remove the Activation Lock. This will require the original purchase receipt from Apple or Authorized Apple seller, then use the link below.

How to remove Activation Lock - Apple Support

Otherwise you will not be able to remove the Apple ID. Resetting the phone will not work, because if that was the case a person could take your phone and reset it, to use it as theirs. This leaves you with proving the device is actually yours with the original purchase receipt, then you can remove the lock.

Original receipt is required. That is the only way to prove the device is yours.

• Having a different device will not help.
• Having the box does not prove it is yours either.

In addition to the great advice posted above, please be certain to tell your friends, your family, anyone you know to never, never, never login to someone else’s account on their device. There is never a reason to do this.

If when you signed out of your account you did not tell it to delete data on the phone then what was on your phone will have been merged into the scammer's iCloud if the phone's settings were to sync your data to iCloud (most people choose to do that).