Disappointed

I ordered 6 X 10kg cat litter and didn't request any alternative for product. Order no ***2. Instead I was sent 1 x 10kg and 5 X 5kg which worked out a lot more expensive. When i queried this I was told that they didn't have stock of 10kg therefore sent 5kg. I called customer service twice and was told that I needed to specify that I didn't want alternative. What was the need to specify? The mere fact that I didn't ask for alternative means that I didn't want alternative. On the whole the 5kgs worked much more and I request sixty60 to reimburse me for additional costs incurred. Kind regards. Very disappointed. N Moosa ***