How do I get the postage cost reviewed

[andremanle-4]

I'm the winning bid for a jacket but I think the postage cost is exhorbitant.  Similar items have recently been posted to me for half the cost from the same country (UK).  I have contacted the seller and explained this and asked her to review the cost, but she has lodged an 'unpaid item case open' without trying to resolve it with me.  I'm pretty sure she must have ticked a wrong button in some way when she was doing the postage costs, but I'm pretty new to Ebay and not sure what she's done.  

How do I get the postage cost reviewed?

If I don't pay, what happens?

Thanks in anticipation of your response