Write a Letter complaining about non-payment of dues

Dear Sirs,

Sub:  Non-payment of dues

This is to bring to your notice that after checking our accounts recently, it has come to light that we have not yet received payment of Rs.14, 800/- (Rupees Fourteen thousand and eight hundred only) for computer harware supplied to you on (date) against your Order No. ---------

Since we never received any complaint about goods supplied to you, we assume that the goods supplied by us have met with your standards and given you complete satisfaction. In fact, it has been our constant endeavour to retain the goodwill of our valued customers, we hope that you will arrange for the payment of dues without any further delay.

Thanking you

Yours faithfully