Crikey!!
How did you stop youself from..... well let's leave that!
Go see a lawyer, first write to the kennels and state what happened and how shocked and dissapointed you were not to recieve a letter of apology for their failure to detect the chip. Express your concern that other dogs from the shelter may have been rehomed when they had responsible owners waiting for them. Also state how much you paid to get your dog back and how upset you are that after taking the trouble to have your dog chipped it was their incompetence that the dog was not returned to you as soon as it arrived at the shelter.
If you get a reply take it and any other paperwork from the shelter to a lawyer.
This is a rare and devastating thing to have happened, please don't let it put you off having other dogs chipped. Always have a tag on their collar too with your phone number and that the dog is chipped on it. This helps a great deal if the dog is lost and also deters thiefs.
Good luck let us know what happens.