Trying to upgrade phone service and it wants to charge an old past due which was discharged in bankruptcy.

Need to be contacted by someone at Cox that can assist with this.  We filed bankruptcy and instead of an old past due balance being discharged my current amount dure was.  The problem is that when trying to upgrade our phone to a higher costing plan it tries to charge me the entire past dure amount that should have been discharged and doesn't show anywhere else in the account... it doesn't show when I go to pay my bill.  Please advise.