Mr Price ridiculous exchange policy

I purchased an item online, however it was too big. I took it within 7days to Mr Price clothing in Canal Walk, however the manger refused to swop it for a smaller size unless I paid the difference. I don't understand why they have a 30 day exchange policy then?? And what made me even more furious is that the manager kept smirking to the point that I actually wanted to cry because I was so angry trying to prove my point and he was more interested in doing other things than listening to what I had to say. I drove all the way to exchange this item and this is the service I get. I demand an apology and also an exchange.. the top was not even fitted and still had tags on it and I had the slip along with the returns page. I am highly upset.. I demand an apology from Canal Walk 's Mr Price manager as that is no way to treat to a customer even if I was wrong. The way I feel right now, I will never want to set foot in that shop ever again!!!