Do not use Woolworths online!

I have now ordered from Woolworths online 3 times, every single time they take the money out of my account twice (the one portion is reserved but takes 21 days to be reversed unless you phone your bank and reverse the amount with them). Twice when I ordered I got a call from a personal shopper asking if they are welcome to substitute a certain product as they do not have it in stock - I agree with a substitution and surprise suprise get charged more than the original order without agreeing to an increase in the charge - the first time this happened the store apologised and refunded me the excess charge - this time it happened again and now they refuse to refund the excess! How can they swop the product (when I was told it is just a different colour) and then charge you more for it without your approval???