Burger King Cavendish double charges clients

Cavendish Branch ****. Their system is down which according to them means that if you pay with card, they need to reverse it, and then ask you to swipe again on a different machine but they deduct the charges for swiping both times and when asking for the charge back, which isn't a lot, but its the principle, they say that that charge is for you to pay and not their problem. Assistant manager has attitude.