Here's the reply I would have sent
UNPAID ACCOUNT
YOU HAVE SENT ME FOUR INVOICES AND I HAVE NOT REPLIED TO YOU YET.
EITHER:
(1) YOU SHOULD UNDERSTAND I'M NOT INTERESTED
(2) CALL ME AT #800-555-5555 TO TELL ME WHY YOU THINK YOUR PUSHY TACTICS WILL WORK.
OR I WILL PLACE YOUR NAME ON THE QUILTING BOARD SO EVERYONE KNOWS ABOUT THIS.