Maintainance

file application for the realization of that amount in court.

Maintenance will be awarded either from the date of application or from the date of order, which the court decides and spells out in its order.  If arrears are there, you should file execution petition immediately without waiting for the final order.  The question is that at  the time of filing the maintenance petition, whether you honestly mentioned that you were working and earning about Rs.20000/- and if so, after knowing that fact the court awarded that amount, then file execution petition to realize the amount.

You cannot claim for the period before your application.

Rightly observed by experts that you will be eligible for maintenance from the date of application and it is the discretion of court to order the maintenance either from the date of application or from the date of order.  Since you already have an order in your hand,  file a petition for collection of pending amount immediately.  Don't keep wasting your time of unnecessary isues or on  misguidance by others in this regard.