1.You were invoiced and given a $0.00 due because you've overpaid a couple of invoices previously and the system applied these overpayments as credits for the invoices. Your billing is correct.
2.These were the transactions that caused the invoices to show as $0.00 due. They covered the balance.
3.From the looks of it, you both signed up for subscription payment, and paid manually as well. This has caused multiple billing instances. We're looking into this further.