Try ringing DHL Customer Service on 0344 248 0012. eBay labels say dispatched as soon as you print them.
If no luck there you might have to cancel the transaction with buyer's agreement (via the dropdown menu for the item on your orders list), and relist for the buyer to buy again so you can start the process again.
If you want to contact ebay you can request a callback on here:
https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid