Is the financial amount earned by the merchant from the bank, as a prize for dealing with it, considered unlawful, knowing that the merchant uses a Visa card and receives his profits from the bank, which is usurious?

There is no religious impediment to collecting the price of goods from the bank via the cards held by customers. However, it is not permissible to benefit from the prize you received for dealing with a usurious bank. You must dispose of it by spending it on charitable causes, and only the principal amount should be retained, as Allah Almighty says: "And if you repent, you may have your principal – [thus] you do no wrong, nor are you wronged."