Customer violating refunds policy by requesting multiple refunds for identincal product

I have a customer that repeatedly orders the same consumable product via my FBA account and then requests and receives a refund.

The product is partially consumed (3 out of 4 items) on each occasion, so I am unable to resell the item when it is returned and am charged for its disposal.

The return reason provided is that the "quality of the product is not acceptable." - The customer is very familiar with the product but is obviously abusing and violating the very liberal FBA returns and refund policy.

I have tried reporting this incident to Seller Central but keep getting advised to follow the following steps

1. Go to Seller Central > Performance > Account Health.

2. Click Report Abuse.

3. Report the abuse through the "An Abuse issue that is not addressed by the other topics in this menu" form.

However, when I follow these steps I get a message back informing me that this is the incorrect way to report such abuse, but I am never provided with the correct method.

How do I go about reporting this customer and getting him banned from ordering from my FBA account?