Are there any provisions to recoup paid child support based on support being calculated on incorrect state approved worksheet?

My child support payments for the past 3+ years have been incorrectly calculated on worksheet A (Primary Custody), instead of worksheet B (Joint/Shared Custody). The Pitt County case worker who has handled our case was provided our Separation Agreement, which clearly outlines overnight custody. I had my children for 150 overnight days in 2014, and are guaranteed 132 overnight days in 2015, both which exceed the 123 days required to qualify for support to be calculated on Worksheet B. 2013's child support was calculated under the same incorrect worksheet. I've struggled to provide an adequate living space for my children because of these over payments. Thank you for any insights you can provide me. Ray Myers [email protected]