Refunds can take a while. The money will return to the source of the original payment. If you used your debit card the money will return to your bank account in about 7 days. Credit card refunds return to card and can take up to 30 days to show up although usually quicker.
If you've already been waiting a while you can contact ebay and ask them. You can ring them or request they ring you by viewing this link on your phone - not on a laptop or PC:
https://www.ebay.co.uk/help/eua?id=5190
