Air pods pro case not charging Apple care returned saying unauthorized modifications

My wife’s AirPods Pro gen 1 case stopped charging for some reason. I took it into the store which sent it away for repairs. It was sent back unrepaired with a note saying that unauthorized modifications were made to it. How exactly does one ‘modify’ an AirPods case? I’m furious as Apple seems to be gaslighting me. The case isn’t cracked or anything so I’m totally baffled by this response. If it’s something else, say so, but don’t tell me it was somehow modified.