If the customer replies to your request but still does not pay, of does not answer at all, you can make a second request. This request still takes the form of a first request but more demanding and less cordial. You may include copies of relevant invoices and statements. You should mention any previous-correspondence and firmly ask for payment in a more urgent tone. Alternatively, you may offer your customer new terms of payment. It is better to collect your money partially than not to collect in al all.