I'm going through this scenario at the moment, seller posted dvd in a postbox with a 69p stamp on, i paid the extra £1.41 to get the item and messaged seller explaining. Now most honest sellers would immediately apologise once they realise there mistake, mine denied it, and when i sent a pic of the stamp he stopped all communication, grrr 😄

Anyway, to cut a long story short, if your seller doesn't refund the extra postage you paid then do what i did and contact ebay buyer protection team and get them to intervene, they're doing this for me and hopefully i get my money back.

Hope your seller is honest and you get the money back,  just sharing my situation, hope it was okay to 🙂