Trucking: Payment Laws, mechanical failure, trucks

Question
We handled 3 shipments for a client that went off without a hitch.  On the 4th shipment, my truck broke down and was unable to pick up.  Now the client is not paying us for the 3 previous shipments due to "cost out of pocket".  What are our options?

Answer
I can't give you an educated opinion, but my moral opinion is they should pay for work rendered and work out something on the 4th load that didn't make delivery on time because of mechanical failure. I'm sure they could have gotten someone else to pick-up the freight and get it delivered. It's not like there is a shortage of trucks. This is not my area of expertise.