Woolworths poor administration

On October 31 I decided to purchase the chocolate promotion (30% discount) via the online channel, the order totaling R258. I received a call stating that a few items were not in stock and asked if I would be willing to substitute them, which I agreed to. I was not informed that there would be an extra charge, so the R258 went off of my account, as well as an extra R313.

If I knew there would be an extra charge, I would have went into a store and got the items directly.

I have now been asked by a representative to contact my bank so that they can reverse the charges. When did the the customer become accountable for your errors?