Failure to deliver despite paying for express door to door

Ordered items from mr price home and paid for express door to door delivery.] The order arrived missing a painting. I phoned immediately and reported it but was told I would have to wait until monday. Nobody contacted me. Eventually at the end of the day I phoned and was told they are doing some internal investigation. How is this of any relevance to me??? I ordered and paid for an item to be delivered express - you can sort out your internal issues at your own leisure. In the meantime, send me my painting!!!!!!!!!!!!!