What to do with a slow pay client or refusal to pay?

We don't typically handle staffing for temporary warehouse but client asked to alleviate their headache ... They claimed to pay $15/hour and said they'd give us a whopping $16.50 an hour to manage and cover taxes/cost for the crew. Crew all made over $600 in 3 weeks and knowing these issues we only offered $10/hour so we didn't completely lose our ***. So we made $6.50 this way as company before costs... Client thinks bc we aren't paying $15/hour we owe then concessions? Plus they have 4 other invoices and well the crew had 1/2 lazy workers as usual who we had to replace. Was a nightmare I had to constantly deal with daily too... Can they legally do anything bc we as a company made our business decision to pay less?