Company used overtime to cover sick days

Is this normal? I have 10 sick days and 15 vacation days a year. I used 2 sick days totaling 16 hours. I also worked 20 hours of overtime. When I received my paycheck I only received 4 hours of overtime. When I questioned it, I was told my sick days were returned to me. This makes no sense to me. This is no different than if I didn't have any sick days and overtime pay doesn't align 1 to 1 with regular pay.

**Update***

I was informed today that the payroll company made a mistake in our companies payroll. I wasn't the only employee affected but rather the entire staff. Unfortunately the fix won't be applied until next months payroll which will probably result in more mistakes but we shall see.

by tylerdurden8