Accounting Abomination

According to Supersonic, when you have paid all of your invoices and you have a ZERO balance, they are still able to reflect an outstanding amount on 30 days and threaten to cut off your services! Customers are invoiced on 1st of the month we'll use May in this example (and NEVER received said invoices in spite of numerous requests), pay the account which is only due on the 1st of June (the following month) on the 3rd of May and get threatened with disconnection on the 27th of May. On checking their portal to download said invoice I see that according to their brilliant calculations I am 30 days in arrears with a ZERO balance. Can someone with some brain matter kindly resolve your dismal accounts!