Don't return the object under any circumstances, until you are happy with their response. I used to work for a food company, and in any case like this, the priority was to obtain the item from the customer, because without it they could not take any independent action. Advise them that it is available for inspection at your house. By the way, if it is something that is easily explained eg a bone in a tinned meat, or a piece of wood in a vegetable pack, then don't get too upset because that is not so bad. Any natural type material is difficult to eliminate. If it is metal or glass, that is very serious. Any food should be metal detected before sealing, and glass is just taboo anywhere near a food plant. Do not deal direct with the manufacturer. Do everything via the store where you bought it.