New Amazon Seller, Issue with refund.

Hi i am new seller who is selling hair care products, I have couple of Amazon buyers who bought my product and refunded every time (3 times as of now) , I did not receive any refunded product back but the refund amount is debited from my seller account.

Is there are way to disable the refund for my product? Or its determined by amazon?

Also how to block these kind of buyers to buy my products back?