How to i open a dispute with a seller which they failed to resolve

[bmi20]

Seller's ad was misleading. The return postage will cost more than the item.  I want a refund and have even offered i would accept 50% but they have not responded

[**peaseblossom**]

Start a return on here:
https://www.ebay.co.uk/help/buying/returns-refunds/return-item-refund?id=4041
select "Doesn't match description" and escalate it to eBay after 3 complete working days.  

If they're in the UK the seller will have to supply a paid-for postage label.   If they're outside the UK they should still pay for the return but it's harder to enforce.