We paid R31.80 for Hot water with lemon....WOW

We are at Wimpy River Square at Three Rivers Mall....we ordered their nice periperi wings with two cups of hot water with lemon...and we were charged R15.90 a cup. We usually eat at Wimpy and have never ever pain for hot water with lemon. The manager said they do charge for hot water and it is in their menu. We asked our waiter to show us that from the menu and it was not there. We've been to so many Wimpy and we have never paid for water with lemon.