Actually if your plan is to irritate them & have them see your invoice/past due letter till the get so sick of it they pay, here's a better idea. I personally haven't done this, but know someone who did under different reasons.

1) Print a two or three copies or more of the pages you want to fax 2) use scotch tape to tape them into a one long sheet and keep a spare piece of tape handy 3) start the fax and as the 1st page comes thru tape it to the last page to create one big circle of paper 4) let this run all night or for any specified period of time of your choosing.

It will burn thru their paper try in no time flat. LOL