They said they’d pay. They didn’t. They’re a valuable client. Try the wording below – it plays on their conscience.
I refer to our last phone conversation where you advised that you would PUT ‘PROMISE’ HERE.
Records indicate that no payment has yet been received.
The arrangement made was made to provide you with some assistance and in good faith.
We trust it was not made in error and look forward to settlement of the balance due as discussed.
This earlier post explains WHY it works so well.