The DIS's address has changed with the server switch, so your ISP no longer recognizes it. It would be like if a friend of yours got a new cell phone and didn't tell you. If you screen all of your calls and only answer numbers that you recognize you wouldn't answer these calls from her because you would think it was someone you didn't know and didn't want to talk to.
Your ISP, and many others, keep hanging up on us, or won't accept our calls.