Consulting Firm Refusing Overtime Pay

Location: Dallas, TX. I was working for a consulting company on a temp-to-hire contract at an hourly rate. Overtime was allowed as long as it was approved by the consultants direct manager. I confirmed this with my contact at the consultant firm, and was told overtime pay wouldn’t be a problem as long as it was approved. For the first time in my four month tenure with them, I had to work overtime due to a project falling behind schedule. I worked 84 overtime hours in total - my timesheet was approved by my manager and submitted to the consultant company. When I received my paycheck, however, they paid me the hours at my regular pay without applying the overtime rate for the hours I worked over. When I emailed them about the discrepancy I was told by the Account Manager that he would look into it and resolve it for me, no worries. I never heard from him again despite seeking updates. Finally someone from payroll emailed me to say this, “This is to inform you that since you come under the CP Exempt status which was mentioned in your agreement. You are not eligible for Overtime Pay.” I never signed such agreement, nor was it ever mentioned to me, I keep all documentation always - so I asked for proof of this signed agreement but have not received a response. I Googled “CP Exempt status” and it said that it applies to salaried employees - which I am not, being exempt from overtime pay under the CP exempt status based on Fair Labor Standards Act. I want to note that there were a few weeks were I did not work the full week (because the they didn’t pay holiday pay and the company I contracted for was closed, or I needed to take a day off for personal reasons) and my paycheck reflected those missing hours because I am not a salaried employee. What recourse do I have to recover my full pay? They owe me one final check because I have moved on from a temporary employee to full time, but still want to fight for my full pay from the consulting company.