You can get in touch via chat and request a block of a merchant. However we can only block certain payments - basically ones where the card is not present.
Some merchants are notoriously hard to block, such as Uber/Apple/Amazon because they use so many different merchant details that once the payment fails they’ll often come back and use a different one and that won’t be blocked.
In that case replacing the card is often a better experience (and in the long run, more cost effective for us!)