Pathetic service

Worst service ever. After taking out a 24month contract. I am being billed 2500 for a 849 package, when I phoned them to rectify the problem they told me its a sales problem so I spoke to the sales department who then told me no I need to contact the accounting department who transferred me to them to sort out the problem. This has been a fight I've been having every beginning of the month for the previous 3months