On the nextel and the Credit card offers your get in the mail. Here is a way to have some fun and get back at them.
Take the little prepaid envelope they give you and stuff it full of what ever other junk mail you have laying around and mail it back to them. They only have to pay for the postage on it if you mail it back and over sized envelopes cost a little more. After awhile maybe they will listen.
Some people are like Slinkies ... not really good for anything, but you can't help smiling when you see one tumble down the stairs.