Lodge a complaint with the Office of Fair Trading - they are usually quick online forms.

Forward a copy, or screenshot and receipt number, of the receipt to Ebay and demand your refund, refer to the previous emails and their promises (make it short and to the point).

Then stop emailing them (stop doing something that is clearly not working) - CALL THEM, and insist on speaking to a supervisor. Refer the supervisor to your email history and the Comsumer complaint, and tell them the payment hasnt been processed, and you want a receipt, over the phone, to prove its been processed TODAY.

Dont get off the phone until youre satisfied. Get the name of every individual you speak to, the department their in, and record the time / date you spoke to them... that will encourage them to actually action it when they can be held personally responsible.

If you have any issues and still arent getting anywhere, follow up with the Office of Fair Trading about your complaint and let them look after it. It might take some weeks, but EBay will reply to them as there are repercussions if they dont.

Ive helped someone deal with OFT the last time I was working in the UK (last year) and they were pretty good.