GFK Mystery Shopping Refuses to pay for completed shops New York New York

I have been a mystery shopping for 13 years.  In all that time, I have never found a company as frustrating as GFK.

I completed five shops for them successfully.  I was attach receipts for each one.  I have never been able to attach a receipt, using either my home or work computer, and either Internet Explorer or Google Chrome; therefore, the problem cannot be on my end.  I do not have trouble attaching receipts to other similar websites.

I completed a shop on 7/20.  I could not attach the receipts.  I emailed the scheduler, twice.  No response either time.  Three days later, the shop was cancelled.  

I emailed the company, asking for help.  Three days later, someone finally opened my email and wanted to know what program I was using.  Silly question. . .since I emailed GFK, I'm guessing I'm using GFK's program.

This person pretended to help and reposted the shop so I could submit.  Same thing.  I was unable to attach the receipts.  I emailed with no response, and three days later the shop was cancelled.

This is a joke, and I should feel lucky that I am only out $20.  Do not shop for them.  If you have technical difficulties, they will not respond.