Should one whose obstacle was theft stop supplicating and performing the Istikhara prayer, knowing that he is trying to return the rights to their owners?

The Prophet, peace and blessings be upon him, made consuming unlawful wealth one of the impediments to the acceptance of supplication. Therefore, this person must repent to Allah Almighty and promptly return the rights to their owners so that their supplication may be answered. They should also supplicate frequently, for it is an act of worship.