Forced to pay for item we did not order

My partner and i were on Durban's north beach late Saturday Night and decided to go to My Diner to have a drink/dessert. While looking at the menu the waiter kept trying to convince us to order something called rasmulla. We said no several times and we just ordered a coffee and a milkshake. When the waiter brought out the order, he brought the coffee and milkshake, as well as a portion of this rasmulla thing and he said "must try". We thought that they were perhaps promoting the item, so we tried some of it but we hated it so left it aside . When the bill came we noticed that we had been charged for the item and asked to speak to the manager. We explained what happened to him and that we shouldn't be charged for an item that we did not order. His response was that because we had taken a bite from it he cannot put it back in their stock, so we have to pay for it. The managers reasoning is ridiculous, as the rasmulla was delivered to our table and sat there the entire time we were there, being exposed to germs, so how could he possibly have reasoned that it would still have been fine to serve to another customer if we hadn't taken a bite from it? We paid and as we were leaving the store, we heard another very vocal customer fighting with the manager over having also been charged for items they did not order. It would seem to be common practice at the North Beach store to add extra items to a bill and then insist the customer pay for it.