I worked in NC and my work hours was anywhere from 45 to 55 hrs per week. However, if I took a day off, I still had to use vacation

I cannot tell from the information you provided if the law has been violated.  If you are an exempt employee, then it would be lawful in some cases to deduct the day from your pay. The employer could have a policy that would allow you to substitute paid time off for the missed hours so you do not lose pay.