They should have sent you a proof to accept and sign for. If the proof was correct, but the ad came out wrong, then you do not have to pay for it. As a matter of fact if you want to get nasty you may be able to sue them if you can prove income loss from the wrong wording. If the proof was incorrect and you signed for it anyway, then your stuck. If they did not send you a proof then I would tell them that you are not paying for the ad if it was not what you sent to them.
Have a Blessed Day,