Call-in centre agent extremely unhelpful

On Sunday 28 Jan I wanted to place an order for a microwave. When I went to 'pay for your order', I saw the delivery address was wrong, and I pushed the 'back' button to fix it. Instead, I received a message saying my payment may have already been processed on my credit card (I didn't fill in the details - presumably you kept them on record). I then phoned your call centre and spoke to the most unhelpful call centre agent ever. It was as if he didn't even try to understand the order. He told me I had to make payment before I can cancel the order, even though your website says "Please contact our Online Support Centre on ***and a representative will assist you in cancelling your order". When I said I certainly would not do that, he said I have to, otherwise the order cannot be cancelled. How is that even possible, and in what world does that make sense? After a useless back-and-forth, he admitted that the order would be cancelled, and said he would 'escalate the matter'. I asked for a reference for the call, and was summarily cut off by the agent. Don't have a call-in centre if your staff are going to be so rude, unhelpful, and uninformed, please.