Billing issues

I have spent months/numerous hours trying to get our billing corrected after buying/upgrading several new phones during a promotion period and adding additional lines and have been repeatedly told by various different customer service representatives that the billing would be corrected and hasn't. 

I can't reach anyone that can actually get it corrected and not sure what else to do besides reach out here. Our Premier Business account has been active for many years and we should have a direct contact, to which I have been told is not an option. We would like to purchase other phones as well and this is keeping us from doing so. Will someone please help or provide a direct contact for me to do so? Thanks.