Billing Issues - Overcharge No Resolution

There has been an error on my bill for more than two consecutive months for charges that are prepaid. The charges are $400 , but reflects as positive. I have sent in remittance coupons / payments to the processing center and to corporate office, yet I haven't received update to my account. I have copies of all. I even received different amounts on my mailed monthly coupon and I brought this to awareness via mail, but I haven't still received any response. Unfortunately, due to this billing error my account has been suspended due to the lack of performance on your department end and mishandling my security interest. I have also filed my complaint with the fcc.gov. If there is no adjustment to my account I will leave no other option to file complaint with sec.gov and further.