getting faxes in the middle of the night ..life insurance sales
number they give to have your fax number removed is out of service

This is what is known as blast faxing.  IF you send an opt-out fax, it just verifies you have a good fax number. They have a voice/fax to e-mail account, usually through International Telcom, Inc who has no information on them other than an IP address, or an e-mail address.  Nearly impossible to track them down.  They just dump that number and move on to the next.  Don't respond either way, they'll eventually drop your number, or you have to change your fax number.

We are receiving faxes that are not asked for nor want. anything to do with life insurance.

Would faxing back several sheets of black paper do any good?
At least it might cost them some money on toner.

No, a reply, if it is answered at all, will not cost them toner. The only machine connected to that line (if there is one hooked up at all) is a computer. As stated earlier, this is another blast fax. The originator will not print copies of anything that is returned on the "removal request" number. The other number listed on the offer for a "customer" to fax back information will also be answered by a computer. Again, they print nothing.