Double billed and no one willing to assist

I upgraded last month, since then I have been double billed on all my contracts for December including new contracts taken out in Nov. I was charged additionally for a 2 for 1 deal. My account is in a mess, I want to pay but no one is willing to look at the billing issues. The store I used will not assist. What kind of service is this? I have been opening calls for a month but they get closed with no resolution or feedback. A month now.