I bought a second hand iPhone and I can’t get in contact with the previous owner

If you can't contact the previous owner to have them log out of iCloud or go to https://www.icloud.com/find/ My Phone and erase the device, then remove it from their account, the device is useless. 

Turn off Activation Lock - Apple Support.      

You have been screwed over and have a brick made pretty glass and aluminium and no money

Sorry to say