Since apple has managed to lose our data, are they responsible for figuring out what on earth has happened on our missing data? they are nowhere to be found, I made hundreds of attempts to find them and I am left aside, missing over a year of data

Then the data was never backed up to begin. It's likely it was missing but not noticed until you restored. You either deleted it or never backed it up. You'll need to restore from your other backups or original sources. Or, if you sync using iCloud, wait for the iCloud sync to complete.

You are responsible for your data. If you've restored from a backup, only the data included in the backup is restored. I've never had an issue restoring so I can only suspect that you haven't been backing up the data or have been using iCloud sync instead (which would be excluded from a device backup but restored after logging in).