Invoice incorrectly done

The worst in the industry,they ignore you bluntly and threatens you by making your credit a mess. We have been dealing with Jacqueline who has no sense of urgency and they definitely make you feel you are nothing. When you email them they have an automatic response that promises you the world and does nothing after that. I am now owing money that I don't even know how the calculations where concluded and we've been bagging for an explanation but no feedback