Bad service incorrect billing

I have been struggling to have my billing sorted out. Customer service is insisting that my bill is double and cannot show me directly which month it is that I am owing. When you call the call centre you don't get assistance the only person who was able to confirm that I am right in not owing is Melanie from collections and yet different agents in customer service via email are not the due diligence and go threw my account with a fine comb. I need my billing to be corrected as I've been threatened with legal action yet no one called me all these months for supposedly owing. I am tired of dealing with client care and the summary they sent has no relation to my account