Been there done that several times. Not quite as bad though. My first was a Sercy 470 that was supposed to shoot 2 inch groups at 50 yds. Shot two 2 inch groups 14 inches apart. Was going on a trip to Africa in a couple of months and needed a gun bad. Called Butch Searcy and explained what I had. He bent over backwards to help me. Sent gun to him and he reregulated the gun twice. All I had to pay was shipping. Thats customer service.
Had a 500 NE that was supposed to shoot 3 inch groups that shot 2 feet low and 3 feet apart. Yes thats FEET. Sent it to JJ at Champlin and he regulated it twice. It now shoots great.
Bought a T Bland that was supposed to be a 375 2.5 inch and someone had rechambered it to 375 flanged mag. Sent it back and they sent me a Merkel for a great price.
Bought another in 40-82 win that cross fired 14 inches and would lock gun up with light loads. Sent it back for refund, which I got promptly.
Have had problems with new Chapuis but seller sent me a new gun right away.
I guess this is the way it goes. Wish people were honest when you pay the kind of money you do for a double.
Don't buy junk and make sure seller will let you shoot gun and have in writing that you can send gun back for refund.
I still love doubles and I'LL probably get a few more dogs before I quit.
Sorry you had the problems you did but glad to know I'm not the only one.

Sam