I can certainly understand your feeling frustrated.You've done a lot to get your computer in working order again,and most of it was not easy fixes.
Just to be on the safe side:Are you having any signs of the original infection?You shouldn`t,after formatting drive C:,unless some of it was accidently restored from backup.
If you are still getting the same error message,perhaps the backup you restored of the program was from a time when the program was already damaged.Would it be possible for you to ask your audiologist about the best way to proceed?I was thinking perhaps a fresh install of the program would be better than restoring from backup.Your audiologist,or your audiologist`s IT person would probably know if that is advisable,being familiar with the program.
How has your computer been overall?Has it been working well,other than the error message from the software to adjust your hearing aid?