Perhaps I have got this wrong, but it seems as though you are trying to involve Initial in your refund and they have no responsibility for this. Deal with Ebuyer, and send them a short but polite letter stating that you want the refund that was promised. Address the letter to Ebuyer [UK] Ltd, 201 Woodbourn Road, Sheffield, S9 3LR. Make sure that a receipt is given at Ebuyers end, so as to confirm the letter was delivered. I would also mention in your letter that you will be taking the matter up with your credit card company, if they do not [ebuyer] shows a favourable response.Pressure or suggesting of contacting credit card companies can help achieve the thing that you are seeking.
Whether the item was cheaper elsewhere with free postage, then this would have been your responsibility to have found this source before deciding to place an order with ebuyer. It as nothing to do with an afterthought on your behalf. Why did Dave at Ebuyer shout at you and your mum!.