This is really a matter for the custodial parent (i.e. your mother) to pursue on your behalf. Absent her being unavailable, you really should leave it to her to pursue as she is a party to the litigation (within which the child support obligation was set) and you are not.
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I agree with the other answer. The CS was intended as a contribution toward expenses your mom was paying on your behalf - a portion of the rent or mortgage, food, utilities, transportation, etc.
Your mom would have to file the motion, but the court would enforce the CS order and make him pay arrears.
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I agree with both Kenneth and David. Leave it to your mom to enforce the support award.
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The mother must enforce it.
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