There is a way to get your information back. I am guessing that you used LINK to do a backup AFTER you installed 10.3.1, right (instead of before you installed it?)
If you did the post-upgrade backup you can go and get a copy of 7ZIP
7-Zip and then use it to open the archive, edit the "manifest" text file to change the revision of the backup back to 10.2.0 or something earlier than you're currently running. Save the text file back into the archive and then use LINK to open it for your downgraded device.
Each backup file is revision locked to the version of LINK that you're using to prevent errors. You may not recover 100% of your information but nearly all of it.