Disappointed in Plaster Sand order (Builders Newmarket)

Disappointment in plaster sand delivered (Builders New market)

I ordered 2 cubic metres of plaster sand from builders and was disappointed in the quantity they delivered. My understanding so far now is that 15 wheelbarrows of sand equate to 1 cubic metre. I had 24 wheelbarrows of sand from the Builders order which was 6 wheelbarrows short. Sounds little but for someone who needed to use the sand it really matters and did impact the progress of my building.

I raised this with the shop and they explained they use Bob cats to load, reviewed the footage with the shop.

My problem is if the standard is 15 wheel barrows, why use a method that does not equate to that.