Do you haapen to have a copy of MacOS High Sierra on an usb drive? You could try to put the image on the Mac from the drive
I would recommend you trying that option, the way I would recommend you doing it is to wipe the drive inside the disk utility option in the window that pops up for you, then restart your Mac. when you restart your Mac if you see a folder with a question mark in it, then you are all set and golden. you should be able to plug in your USB bootable stick inside your Mac and it should instantly start booting up, it will prompt you to install instead of update.
If you have another Mac that you could steal the image off of, you can download MacOs High Sierra from the Mac store and when the launcher is inside the applications folder, then insert your USB to make it a bootable, go into your disk utility under launchpad and rename the thumb drive to "untitled12" then open up the terminal application and run this command:
sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled12 --applicationpath /Applications/Install\ macOS\ High\ Sierra.app
you will be prompt to ender your password, and then the terminal prompt will make your USB stick bootable to get your Mac up and running in no time!