Online collection mess

I bought a stove online and paid for it about a week ago. To avoid delivery costs I sent my own driver to collect the stove yesterday. Apon arrival he was told that the money paid was short as the stove was no longer on promotion and I had to add more money for them to give me the stove. My driver gave me a call so that I can explain to the man assisting him, that I had bought the stove online and it was on promotion at the time of purchase. He then set my driver to the online department whereby he was given a number for to call a person by the name Danny who will explain to me what is going on. I called makro online today and they were very surprised as my order is packed and waiting for me. I called crown mines and they also confirmed my order. My only problem now is who will be liable for all these petrol costs because makro charges for delivery and due to them I have to pay my driver again to go back and collect the stove. In the meantime, I have to deal with an angry tenant of home I promised that he will have a stove by 16/04/2018.