How to politely chase overdue invoices

I would like to add a format that we use effectively;

Hello XXXXX,

We noticed by this morning that no money has cleared. We are a small business that relies on our client's integrity and would be obliged if you could advise on when we can expect the money paid for the invoice 12345678/82-QB (copy attached). The invoice is now XXX days overdue. In the unlikely event that the invoice remains unpaid after 30 days from issue, This then becomes a delinquent account.

I could start calling XXXXXXX myself but I would probably get any number of the wrong people; so could I ask you to do me a favour? It would be simpler and probably more productive if you could oblige me by contacting the person responsible for authorising payment and asking them to expedite it soonest?

I await your advices.

I'd only add, with some customers it's best to invoice them on a pro-forma basis, and save yourself a lot of hassle.

Great advice. I’ll save this for next time I have an overdue invoice. Thanks for sharing.