Why Sprint and Comcast annoy me!

I'm certain I am not the only one who finds both of these companies so fantastically frustrating you almost have to laugh.....
I moved recently. I stopped Comcast over the phone. I was told a specific amount due and when I went in to return the equipment that amount was confirmed by two employees at the Comcast center off of Broadway. I paid it and was told I was done. Guess what I got.... not only did they NOT turn off my service and have billed me for another month, but they also say I have an unpaid balance due beyond that additional month. I call... again. I am told by a very nice guy that "they must do things differently in Denver" and that he would call me back in a few days (after his days off) and let me know "what I still owe". I informed him that I would be paying nothing more to his fine company and that this is their mistake. I never heard back from him, and I just got another bill. They can bite me.
Sprint... ah Sprint. I guess you just can't let me go. I paid off Sprint and got a nifty letter and confirmation number stating so even. Guess what. Yep, they say I owe them more money as well. I call... again. I get someone who is confused and transfers me to another dept. That person is also confused but at least can see on his screen that yes, I have paid it off. He says he's sending me another copy of the same letter and that should do it. I say, "How so? Your company doesn't acknowledge the letter they sent me stating I had paid in full." He says, "Well, it makes no sense to me either." BTW he is the supervisor....
I swear to God if either company sends me another bill you will hear my fit of anger in space.