WHAT IF PREVIOUS OWNER IS USING IT FOR A DIFFERENT PHONE

If the person selling you the phone is the original owner, have them contact Apple. Apple can remove the Activation Lock if provided the required paperwork. Either take the device, the original purchase receipt with the serial number, and a photo ID to the nearest Apple Store (if it has reopened)

Genius Bar Reservation and Apple Support Options - Apple.    

or contact Apple ID Support. 

 Apple ID - Official Apple Support.    

Contact Apple for help with Apple ID account security - Apple Support.  (Link doesn’t always load)   

Get Support      Work through the screens to get a chat option. 

Apple Support schedule phone call

https://twitter.com/AppleSupport       People have posted it may take an hour or more to get a response.

It doesn't matter.

Activation Lock is a theft deterrent feature with no bypass or workaround.

Without the owner's authorisation, no thief or anyone including you can re-use the device.

Note: Using all CAPITALS in online forum are considered very rude and that you are shouting.

Only the correct Apple ID & password can release the lock, nothing else.