Translations / Refuse/delinquent payment

RX Medco had hired our company to provide interpreters for a few of their work cases. We sent them contract agreements which clearly stated the pricing and payment schedule for our services which they had signed and sent back. It has been a few months since we had spoken to anyone in their accounting department who coincidentally are the only people in the entire company who can authorize payables. They owe us quite a bit of money for a number of open invoices. We highly suggest not working for or with this company.