"I've been told it will be cancelled and refunded automatically so I will be keeping a close eye on it!"

If it's Seller pays postage, the seller needs to request the refund of an unused SD label.

If it's Buyer pays postage, the buyer should be refunded automatically after 30 days.

https://www.ebay.co.uk/help/selling/posting-items/setting-postage-options/simple-delivery?id=5575#se...