First, Disney has never sold chewing gum, because they have never wanted to clean it. Makes sense to me.
Second, if a large corporation has a problem paying, it is typically not a corporate problem, but an administrator problem. Sometimes the administrators won't process the bill, sometimes they lose them, or sometimes they just forget. There is also a possibility that you are doing something wrong in your invoice submittal process that does not expedite the process. That is why, when you are doing a project for a major corporation, you need to define the payment terms, and what is expected of you, as a contractor, in order to receive timely payment.