How to unlock activation lock without previous owner?

You cannot. You'll need the owner to unlock it or the device is useless. (https://support.apple.com/en-us/HT201441)

You'll have to get in touch with the person who sold you the device, or recycle it responsibly.

Then you should responsibly recycle your device. There is nothing you can do.

the owner sold it to me on face book and never took off i phone locked to owner

I bought on Facebook ,I asked him but he blocked my Facebook.

Noway to contact the person