You're in a tough spot, it seems the buyer is unsatisfied with your work and that's one way to cancel the order.
I suggest that you reach out to the buyer and try to understand the root of their dissatisfaction. If the buyer remains insistent, you may consider contacting support for assistance in resolving the dispute.
It is important to remember that your hard work and effort should not go to waste and if you believe that your work is up to the standard and the buyer's request is unjustified, support may be able to help you resolve the situation in a way that does not negatively impact your profile.