How difficult can it be to deliver 6 of the same items?!

I ordered a bulk special of 6 x 3kg Bio Classic washing powder and only 4 were delivered. Immediately sent an email and mentioned it in my feedback, and have called customer care twice, but have still not received the promised feedback nor delivery more than a week later. I don't understand how difficult it can be to schedule delivery for the remaining two items, or to arrange collection from the store. ********** service. Will never order online again.