Hello!
To not be concerned about saving issues, it is often handy to have a backup of your save file, and you can still use Steam Cloud too if it's useful to you. You may try loading the newest auto save in-game, or other saves. Also mind looking into the "Euro Truck Simulator 2" folder inside Documents, and watch for the "profiles" and "steam_profiles" folders in case you can find the save there.
If the earlier doesn't work, since you lost your progress, you can edit your current save file and add the necessary levels you lost, and also edit the odometer of the truck if you'd like. (Make sure to back the save up prior to that).
There are many tutorials on save editing, such as this one, that might be practical for your case.
It'd be a great pleasure to hear if this was of any use. Thanks.