Did you personally have any paycheck where you were paid less than minimum wage after adding in the sales commissions? It is not uncommon to have such a pay structure of a lower hourly rate than minimum and have commissions make up the rest of (or more than) minimum wage. It can be a common compensation technique for those in sales positions and if you don't make enough sales/commissions to make up the difference, generally you will not keep your job.

You would only have a case if you had a payweek in which you could take your total pay and divide by the total # of hours worked and have that result be less than minimum wage/OT.