Disappointing service

I ordered groceries from checkstar overport via Watsap on 29th July, one of the items being 6X 5lit oil. I was told that they had only 2 oil in stock. I confirmed the order which was delivered on 30th July. 2 oil, 2 pkts with other grocery and 3X8kg dog chunks. 2 days later I removed till slip which was in one of the pkts and noticed I was charged for 6 oil. When I queries this overcharge for 4 oil I was told that they will deliver d 4 oil. Later in d day I received a call from pranita from checkstar stating that the 6 oil went out of the store and driver said he delivered the box of 4 oil. Pranita said to give her 2 days as she's going to investigate this matter. My question is how she plans to do that since the box of oil, if left the store, disappeared on route and why has it become my problem that i have to wait for 2 days for her to investigate? I've paid for something that wasn't delivered to me and want to be reimbursed asap. Very disappointing service. Nasreen Moosa ***