What do you do when the seller won’t cancel your order when you request it?
Accept the NPB penalty. Won't hurt you unless you make a habit out of placing/canceling
orders.
There are valid and invalid reasons stated in this help-topic: https://www.bricklink.com/help.asp?helpID=79
From there you can click through to Problem Centre order for the next steps.
What do you do when the seller won’t cancel your order when you request it?
Accept the NPB penalty. Won't hurt you unless you make a habit out of placing/canceling
orders. Making an order is Legal binding contract according to Bricklink rules and you should always pay. It takes time to pull orders and bill them out plus a person with principles pays for there obligation.