Dear Sirs,
Our books of accounts indicate that your account amounting to Rs.________________ has been running open over six months. Will you please look into the matter and send us a cheque for the said amount.
We enclose a copy of our catalogue introducing certain new products and rise in prices of certain existing products. Since you have not placed any order over these six months, we hope it would pay to replenish your stock now.
Yours faithfully,