My previous number at work was exactly one digit off from the local Department of Defense office. I got about 3 calls weekly for them most of the time. Until the DoD issued a letter to certain people asking them to call my number. I called the DoD informing them of their mistake for the first two letters. When the third was sent, I had my office number changed.

Good luck to you, but I think the only way to get a resolution is to change your number.