$400,000 in withheld funds is not the sort of thing you should just place on the back burner and ignore while your client fumes. It is business malpractice, the sort of thing you could get sued over and be penalized heavily for, if not merely lose your customers and blacken your reputation everywhere. Businesses that do not resolve problems like this in less than twenty four hours deserve to go out of business.
This of course can backfire via social media into negative reputation and some repeated bad behaviors can landslide into class action.
But large companies are willing to accept such risk and will continue such pattern.