The high cost of being reasonable!
There we have if folks. If your terms are 30 days and it's already gone to 60 with nothing in hand, no definite commitment to pay within a particular time frame, and they won't answer the phone or return calls, then your being reasonable.
I prefer to be unreasonable, especially when there's no logical or otherwise compelling reason for me not to be. I communicate my intent to immediately commence litigation with the shipper, receiver, and any other party involved.