Saxby centre Spar

I am extremely disappointed in the Spar at the saxby centre, after advertising a special (buy and get 2 boxes of 6 long life milk delivered, you get one box free) i get called after 6pm to be told that their delivery capacity has veen reached... after i placed the order AND PAID for it earlier today. I was told that they can still deliver tomorrow but then i dont get the free box....i feel that i ordered today, and paid today on the day of the special, its not my fault they cant deliver today, i feel like my side of the transaction was done correctly, and according to the stipulations. The fault is on their side, yet i miss out. Sure they say they will cancel it and my money will be refunded, but the point stands that they made a offer and couldnt keep their side of the transaction yet i get penalized. Again i am VERY disappointed in a otherwise great store