Actually, I'll bet if you read the original order, you'll find that it includes interest accrued until paid in full and possibly attorney's fees. What payroll does (or should do) is, when you get close to the original amount of the order, they call the court and get a new amount to account for interest. A new order does not have to be issued for the additional interest.
Does your paystub show the goal amount yet to be deducted? If not, how do you know about the new goal amount? Have you asked payroll?