You can send a cancellation request the the seller but they have to cancel it as a buyer does not have a right to cancel.
Go to the item in your PUrchase history and see what it says there.
If it says Refunded then them money will go back to scource. If it was from paypal then it goes back quickly. If a debit account it can take 7 days and a credit card can take up to 30 days to show on your statement
If not
You needed to open a not received dispute
Go to the resolution centre at the bottom of the page and see if the option is still open for you to open the dispute.
What is the latest estimated day of delivery on the listing
If you have not recieved your item and it is past the latest estimated day of delivery on the item description
then you can open a not recieved dispute one day after the latest estimated day of delivery on the listing.
You can do that at the bottom of the page under Resolution Centre
Escalate it too ebay after 3 full days
https://www.ebay.co.uk/help/policies/ebay-money-back-guarantee-policy/ebay-money-back-guarantee-poli...
You have 30 days from the latest estimated day of delivery on the item description to open a dispute.
Failing that.
contact ebay then top or bottom of the page under Seller help or help and contact
Scroll down for contact details
It will be call me back or chat with us
