Even better do what I did, fill a large envelope with old fag ends, seal it up and put their address on the front , then mark it 'Payment enclosed please open with care' Then post it but most important DO NOT PUT A STAMP ON IT.
The postie will deliver not deliver the letter until they pay for the delivery and the fee for no postage, they see the the Payment enclosed note and end up paying £5 for a load of dirty fag ends.