Got paid for half my work

My last work order for Project Ivory showed only 4.75 worth of hours when I worked 10. I immediately sent them a zendesk request, and they got back to me saying we only get paid for what they deem acceptable. Nowhere in the emails did it say we wouldn't get paid for tasks they thought weren't good enough. My first batch with them I got paid for every task, so I doubt all of a sudden 5 hours worth of my tasks were terrible. They're also supposed to give us feedback, but I never got any. They were very vague in their wording, as they always are, and provided no real examples of what I did wrong. I have screenshots of all the work I did and sent them to them but they don't care and won't pay me. So I did 5 hours of work for free basically. This company has always been shady, but they've always paid me up until now. Is anyone else dealing with this?