I doubt that the 'company' sending you the letter can even do a fraction of what they promise.
Seems that the BBB agrees with me!
I wouldnt even call to stop the mailings. Let them spend the money on the stamp! The sooner they are broke, the faster we are all better!
And if the mailing comes with a return envelope, stuff it full of junk mail and send it back, for them to pay the postage. (I did this several times with some politicians' fund appeals, and I finally was dropped from their lists.)