Auto repair shop made repairs beyond the scope of the appraisal. Damage fixed was actually excluded in app report. Shop wants me to pay difference.

I am a lawyer in CT and practice in this area of the law.  The shop did work that it was not required to do and is not permitted to be paid for the work absent your consent to have the work performed.  I suggest that you explain that and then hire a lawyer to sue the company if they do not return your car.  If you have your car, i would ignore the calls and make them sue you in small claims court and then counterclaim for them filing a vexatious lawsuit.  If you are sued, consult a lawyer to implement the foregoing strategy.