Leak in the wall within a week of bathroom remodel. Looking for advice

The bathrooms are on the second floor. Noticed a leak when toilets flush in the garage below. They came back, opened part of the wall and are claiming an old water line connection broke. Like nothing they did caused the issue. How do I go about getting a second opinion on this? My fear is they will close the wall, and I will have mold/structural issues down the line. There is water in a good 10 foot portion of the wall that leads from the bathroom down to the garage