Paying for their stock errors.

They have twice delivered the wrong size item on my order. When I returned the first item, they wanted to credit me for the item - but not the delivery fee of R65 - when it was their mistake not mine. I also wanted a replacement - in the correct size - and not a refund. I was told there was no stock, yet I could still place the order in my trolley - and stock was reflected. So I queried both the non-refund of my delivery fee and the stock that showed online. They then decided they would send me the correct size. But lo and behold, once again they have delivered the wrong size. Part of the frustration is you cannot call them - they communicate only via email - so it takes 36 hours for them to respond. Two weeks have lapsed since I placed my original order - and I still have nothing to show for it.