I have to pay more to change a size

I bought a pair of shoes from Woolworths online and they delivered but the show is a bigger size and I wanted to change the size and they are refusing for me to change the size but I am required to pay more money for the same shoe because the same shoe is not on special.

I think this is a ******* especially because it is the same damn shoe.

I am very disappointed with woolworths about this.