Taking money *******ly

I recently change my flights (changeable) when 2 days later BA calls me to say: sorry, you were given wrong quotes & we need to charge you the difference (~$100). I didn't agree, stating I made a decision based on the fees agreed with the contact centre consultant, asked them to listen to the recorded calls & to absorb the cost based on the fact it was a mistake made by a BA employee. They agreed. A few days later, I see they charged me the additional fee via my credit card. I would've expected BA to treat me with the same courtesy & respect I do them: I pay for my service when I need to. I do not ***** from them. This is unacceptable from an international company that we all know so well. Where is the customer service? Also: we asked for things 3 times during our flight home which 3 different air hostesses forgot about. Unacceptable.