Wont take the knock to satisfy client after mistak

I called Netflorist Call Centre today as I received a free delivery voucher that could be used today only. I had tried endlessly to order on their website & was having problems so decided to order telephonically. After mentioning to Cindy when she told me the amount that it was incorrect as I have a voucher we finalised the purchase only for me to see on the sms that came through she had charged me the delivery. She then informed me that she cant do anything to fix it expect offer me a voucher for future which defeats the purpose or give me nougat that is already in the hamper I ordered so that is pointless or else a stuff bear for my 65yr old father - I THINK NOT. She then said I could call Discovery & cancel the purchase then call back and re-order. So the client is to do all the work for your mistake.??? Discovery said that they can do nothing Netflorist needs to do a refund so I call back & tell Cindy that they can give me Lindt chocolates extra & that will be a loss of R 20.00 for them which I think they could take the knock as it was their mistake & I had to do all the work. Suddenly a refund could be made -Strange that. She did apologise but what happened to customer service