Advice

I left my other job about two weeks ago, the office manager and I didn't get along and I'm positive that's why I was fired. Anyways, I was paid salary from the time I became an employee, 36 hours a week, no matter if I worked 44 or 20 I still made the same. I work in a dental office and I got work done on my husband's teeth and was going to pay it with my last pay check, the boss knew this. Well the boss' wife usually does payroll but they were out of town last week and the office manager did it, or at least I'm assuming she's the one who did it. Well instead of getting a check, I got a piece of paper stating that my bill was 368, I worked 18 hours (I'm salary....) at $15 an hour (which is much less than what I was making if you did the math!) and that my paycheck didn't cover what I owed and I owed them $140 ? which doesn't even make sense. I need kind ideas on how to handle this, my goal is to go to the boss and ask him what's going on and why I wasn't paid my usual 36 hours at my usual pay (which would more than cover my bill and send me home with money) but is there anything else I need to cover? I feel like I'm going to get tunnel vision, get upset and lost my composure.