Have you opened a case for item not as described and entered that tracking number into the case? If not do this now:
You then go right of the item in your Purchase History, and from More Actions select Return this item, selecting the reason... Item Doe Not Match Description or Photos.
The seller has 3 days to accept the case, if they don't , you need to escalate on day 4, or within 30 days, and eBay will step in and force the refund.
Enter the tracking number of the item sent back into the case details. On receipt of their item they have 48 hours to refund you. Again, if they don't, you escalate the case.
Do not close the case early for any excuse or promise the seller may give, and do not forget to escalate.
@bobr_4473