repay (one) by (doing something)
1. To do something as a means of providing compensation to one for some service one rendered or debt one is owed. Thank you so much for your tutoring! I'd like to repay you by helping with your packing ahead of your move next week. I don't have much money, but I can repay you by designing a new logo for your store, free of charge.
2. To do something that exhibits or indicates a complete lack of gratitude, regard, or esteem for one. (Sarcastic or ironic in its use.) I've devoted my life to raising you kids, and you repay me by stealing my car and all my money? Tom moved his entire life across the ocean to be with Sarah, and she repaid him by cheating on him over and over again.
3. To do something as an act of vengeance or retribution against one. The principal humiliated me in front of the other students, so I repaid him by putting sugar in the gas tank of his car. We're finally ready to repay this dictatorship by blowing up the palace and retaking the country for our own.
repay someone by something
to recompense someone by doing something; to settle a debt with someone by doing something. I will repay you by cutting your lawn free for a year. How's that? Can I repay you by taking you to dinner?