Ah, now with AmiAmi, they are clear about their policy regarding preorder cancellations. Nippon Yasan is not, and does not offer you the opportunity to cancel an order outside of raising an incident ticket. No site has the ability to hold you to ransom to pay for something that you no longer require - the common move seems to be a spiteful threat of banning you as a customer, which is really backwards. For one thing, I have spent a lot of money with NY over the last year or so, so if they carry on down this road, they'll lose a lot of potential future business from me.
I understand their needs as a business, but I have tried to be reasonable by giving them plenty of notice so that someone else will have the opportunity to buy items in my place (some of my preorders are sold out, so the demand is obviously there). They've stated that if non-payment occurs on any preorder, they will terminate the account - I don't have payment details logged with them (I don't think you can?), so if they wish to remain silent (even though I have chased them after their abrupt response), the preorders will go unpaid and it'll be time to say goodbye to N-Y.