For what my opinion is worth, whoever did the work is a hack and not a gunsmith; and personally, I'd be mad as hello at what was done to my gun. And from my personal experience, if this guy did this poorly the first time; don't think for a second that a do-over by this guy will yield a better result. The correct way to repair this stock is to splice wood onto the ruined areas as already suggested, then inlet the side locks. After fitting, a professional can blend the repair so that it's undetectable. As other posters have suggested, Bill May would be a great option to consider as he's repaired several Smith and other make stocks for me and does incredible stock repair. I won't speculate on cost, but Bill's always been fair with me.
I'm assuming this is a special or favorite gun; and if it were mine, I'd be insulted with any suggestion to sell or trade. The bottom line is that you made a bad decision using this gunsmith; so use this as a learning experience as you pay for and obtain for PhD in vintage double gun collecting. I've screwed up similarly many times myself, we all have; and assuming this is a special gun, my suggestion is to bite the bullet and pay for a proper repair whether doing so makes dollars and cents or not. Clearly the first gunsmith will be no help. Certainly, you should attempt to get some reimbursement if possible; but whether you do or not, resolve to avoid this outfit at all costs going forward. Good luck!