You could email them and say you need it collected by a certain date. If they don't reply or don't collect by then you can cancel the transaction. Or you can do that right away if you prefer.
Go to the dropdown arrow alongside the item on your sold page > Cancel order > Something wrong with buyer's address, which is the nearest one to this situation as it's possible they are too far away to collect easily. The refund will be issued in the process.
And put their ID on your blocked bidder list:
https://www.ebay.co.uk/bmgt/BuyerBlock
