If you shopped for Checkmark inc. you may be getting scammed. They seem to be playing hide n seek with the shopper payroll.
I highly recommend shadowshopper. They are an excellent source of mystery shop jobs. They are also a good resource for getting yourself registered with mystery shop companies. Most mystery shop companies pay out around the 25th of the month following your completed mystery shop.
What company didn't pay you??? & When did you complete the shops.