Wrong info and wrong billing

Went to Wimpy The Avenues Springs yesterday with my daughter for breakfast. When placing my order me and my daughter asked Busi twice about the buy one coffee get one free, we specifically asked her if I buy one and we get one free if my daughter can have it and she said yes. Twice we asked it to be clear. When our bill come she charged us for 2 coffees. When I queried it the cashier called Busi which then said but we did have 2 coffees. I told her that I asked you twice about the special of the buy one coffee and get one free. She then changed her story and said she was not sure and only was told later that you have to buy 2 coffees and then get 2 free which is ridiculous cause we do not want to have 4 coffees. She only said SORRY. I mean really do they not get proper training before a special starts in order for us to get correct info and decent service. If we knew that my daughter would have ordered a milkshake or something like that instead. So upset...