if a company repairs something without my signed permission and extorts me for960$ for it s return are they breaking a law?

I sent a guitar to Gibso in January for a tuning peg. They said they hadn't opened the case yet 5 months later and later admitted it had been in the factory and never sent to the repair factoy in another state. they replaced a single tuning peg and I must pay 960$ for it's return. I never signed any release for them to make the repair. This deepened my already treated for thirty years depression and kept me bedridden for that time and caused thefirst problem in a perfect 14 year relationship . I'm Sure one must sign off on an estimate for a repair before it's done. Is this extortion? Is it illegal ? Is it better to sue in small claims court and take five thousand limit or should I obtain a attorney and go for pain and suffering plus dropped repair charges? If this was a against the law who would I have arrested? I'm 70 and in terrible health and I love that guitar . Or does company mean I have no rights and must pay 960$ for a tuning peg. Gibson used to be a decent company while les paul was alive, but have become corrupt sinc his death.