Is the grant money disbursed to PhD students every three months considered unlawful if the student's admission to the PhD program was obtained through cheating?

Cheating is forbidden, but since you have already begun your studies, the way to repent from it is to regret it, resolve not to return to it, frequently seek forgiveness, perform good deeds, and sincerely dedicate your intention to Allah in your studies. You should not abandon your studies, nor is it forbidden for you to benefit from the scholarship.