Q: Help me please!!!

You need to contact the seller and ask him to remove this iPhone from his list of devices. Otherwise, your iPhone will be a useless brick.

Find My iPhone Activation Lock: Removing a device from a previous owner’s account - Apple Support

Apple will not help to unlock the device locked with previous owner id. Try  find other ways to contact the previous owner. Some user also report the issue when the phone is asking for unknown id after the update. This may be your chance.

If you can't activate your iPhone, iPad, or iPod touch after installing iOS 9.3  - Apple Support

If you can’t activate your iPad 2 (GSM model) after you update to iOS 9.3If you can’t activate your iPad 2 (GSM model) after you update to iOS 9.3

Apple halts iOS 9.3 updates for older iDevices due to growing Activation Server Lock issues