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You have a file number if you are a beneficiary of the Social Solidarity Program or if you owe an amount to the Ministère de l'Emploi et de la Solidarité sociale (MESS) (debt you are repaying to the Centre de recouvrement). You must indicate the file number when you complete the change of address request on line. The number is indicated on the correspondence you receive from the Ministère. It has 4 letters followed by 8 numerals (e.g. ABCD12345678).