Q: No iCloud no password

https://iforgot.apple.com/password/verify/appleid

Unfortunately, you cannot do very much with your phone unless you get assistance from the previous owner, they should either provide you with the password to unlock it or remove their account from the phone entirely remotely through iCloud.com > Find My Phone.

If you aren't able to get assistance from the owner and are unable to get a refund for your purchase, please dispose of the device responsibly by sending it for recycling.

There is absolutely no way to ever unlock an "activation-locked" iPhone.  If you get a run-around from the seller, it is very likely that you have a STOLEN iPhone.  This feature is intended to render a stolen device totally worthless.

Tell everyone you know  ---  stop buying stolen stuff.