(a) the amount collectible in any month shall not exceed ten per centum of the assignor's future earnings payable in such month;
(b) if at the time of the filing with the employer (1) any other assignment of future earnings is subject to payment, or (2) any garnishment against such earnings or order against the assignor for installment payments to a judgment creditor, is in force, no amount shall be collectible while such other assignment is subject to payment or such garnishment or order is in force;
(c) no portion of future earnings shall be withheld from the assignor or paid to satisfy such assignment in whole or in part while any portion of the indebtedness secured by any valid assignment securing or relating to an indebtedness aggregating less than one thousand dollars, previously filed with the employer in accordance with this section, shall remain unpaid. 3. No portion of future earnings shall be withheld from the assignor or paid to satisfy in whole or in part any subsequent garnishment while any portion of the indebtedness secured by any valid assignment securing or relating to an indebtedness aggregating less than one thousand dollars filed with the employer in accordance with this section shall remain unpaid, but nothing contained herein shall exempt the earnings of a judgment debtor from the application of an order for installment payments to a judgment creditor.