Those are the rules,  a seller does not have to accept a cancellation request.

The item has not been physically dispatched but when a seller triggers a Simple Delivery postage label, it automatically marks the item as dispatched.  Don't blame the seller for this,  is an eBay quirk with SD.

What do you mean by ' payment method wrong' ?  Did you have an invalid credit card on your eBay account,  then the payment will not go through.

@steponavicius20