Terrible customer service

So upset with customer service. I was given wrong information by the service centre on TWO occasions and they are refusing to admit it or repay me the extra money it cost me. Swiss Air’s excess baggage fees are already ridiculously high when compared to other airlines. They promised that I could just pay a small difference in fees at the airport to upgrade my bag. The airport would not let me do this but charged an extra £100. However, I was told on the phone I could get a refund. I am now being denied a refund and am furious that they will not even discuss it or listen to their tapes showing that I was given incorrect advice.