How to activate a used iPhone bound to another account (already removed from iCloud)?
You mention that you removed the phone from your Find my iPhone in iCloud, but then it can't be activated with anyone's Apple ID. Only the Apple ID that is shown on the page is the one that can be used to activate it. Once it is activated, you can use any Apple ID to register the iPhone and log in to iCloud.

In the screenshot above, only the Apple ID matching e•••••@gmail.com can be used to 'unlock' the phone. Make sure that this is the Apple ID that the device was removed from in Find my iPhone.

Once you have removed the phone from the relevant Find my iPhone account, try rebooting the phone. This should force the device to re-check Apple's servers for the Find my iPhone status of the device. If this fails, simply use the Apple ID that you removed the device from to activate it, then you can set it up normally.