Evaluation Solutions They won't pay. Internet

I have completed 5 BPOs for this company and have not received payment.  One is over a year old.  They call at 7:00 p.m. at night and expect the report back the next day.  When I tell them I cannot work for them until I receive payment for work already done, they tell me that they will put in a payment inquiry and I will hear from someone very soon.  I have received several follow up e-mails stating that they have escalated my account for further review and that it is in process.  They also state that an additional e-mail will go out to let me know that the payment has been mailed.  That e-mail has never arrived.