perhaps a silly question but what do I do when item not received?

[IHeartIona]

I have used ebay for a few yrs but never not received an item before. Bought a book mid Aug and haven't got it yet. I emailed the seller and she said she had posted it ten days earlier.
It must be lost in the post - do I just lose my money or does she need to send me the proof of postage so I can claim with the royal mail? And do I need to do the item not received thing through ebay or is that only for when the seller has no proof of posting?
My dh seems to think I just have to put up with it and can't do anything...

thanks for any advice!

yup, message seller again and ask for a refund. Then, if you don't get a refund file an item not received dispute.

They need to refund you and then they claim from the RM

great, thanks for the advice!