Apple ID has been locked for security reasons

It is the previous owner's responsibility to make sure the phone is ready for your use. I am not fully understanding the issue here but if it involves needing the previous owner's account information then the previous owner needs to do the recovering of that, not you.

What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support

Here are additional resources for the previous owner:

Help with a lost Apple ID or password:

• "If you forgot your Apple ID" [this is likely an email address you are using or used in the past] click here --> https://support.apple.com/HT201354

• "If you forgot your Apple ID password" click here --> https://support.apple.com/HT201487

If necessary and you are willing to wait, Apple can completely reset a device if a person can provide sufficient evidence of valid ownership. Do this online at: Activation Lock support request - https://al-support.apple.com/#/additional-support Apple says, "Proof of ownership documentation is required," but does not state what currently constitutes proof. Prior to this new online service Apple typically required the original receipt issued by Apple or an Apple Authorized Reseller and documented provenance (so typically it would be the original owner who does this, or a descendant with legal proof of ownership).

See the Apple Support article(s) below. 

If your Apple ID is locked or disabled - Apple Support.    *

If you have changed your ID or password, have you followed the steps in this article? Make sure you turn of Find My Phone before signing out of the old ID. Once signed out and Find My Phone is off, then sign in with the new ID.

What to do after you change your Apple ID or password - Apple Support.  *

If necessary, contact Apple ID Support for assistance.  See the Apple Support articles below for contact information.  

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. You may have to pick a slightly different problem.

Apple Support schedule phone call.   -

If necessary, try Twitter

https://twitter.com/AppleSupport.    -          

From the Apple Support article below. 

Without proof of your identity via security questions and other carefully selected criteria, Apple Support can't help you reset a password or perform any other actions on your account. These policies are audited and reviewed on a regular basis.

Security and your Apple ID - Apple Support.      *

If necessary, if the previous owner is the original owner, have them contact Apple. Apple can remove the ID  if provided the required paperwork to include the original purchase receipt with the serial number on it. 

Request additional support for unlocking your device.    -

You used to be able to take the device, the original purchase receipt with the serial number, and a photo ID to the nearest Apple Store (if it has reopened) and have them remove the ID. This may have changed, so have them call the store before going to make sure they can help.

Genius Bar Reservation and Apple Support Options - Apple. 

You are welcome. Do they have the purchase receipt so they can ask Apple to remove the ID? I suggest you ask for a refund since the phone is worthless to you.

If the store is an Apple Authorized Reseller, the receipt should be accepted.