Barbara,

File this one under "moral conduct".....you must first resign yourself to the fact that this company is no longer going to use you.  Rest assured, it is highly impossible for such blatant mistreatment of a vendor to be overlooked in an attempt to dare ask you for your services again.

Having said and acknowledged that, you MUST, morally, do whatever you can to help protect the next vendor from additional mistreatment/nonpayment of services. 

You will not only sleep better at night, but also afford others the opportunity to do so as well.  Finally, the record will show that your company will NOT accept this type of business practice and will forego future potential revenue in exchange for doing what it right...best of luck to you and your staff...JT