I was going to recommend the same thing, but I also know there are plenty of AR companies out there. YC even funded one called YayPay. I know my accountant will chase down invoices for me if I asked him (for a fee of course), thankfully QuickBooks Online handles this reporting, and has a one click solution to resend Invoices. I don't do $135k/mo, and only send a handful or two of invoices each month, so I cannot comment on how well it scales.