At first, the calls were bearable, though numerous and sporadic. Some interruption while Langly was trying to work wasn't anything new. It was annoying, but amusing to see the system failing to keep the imaginary money.
However, being harassed about someone else's outstanding (in almost every sense) student loans was not his cup of (insert caffeinated beverage). Nor was it fun to continually explain he was not covering for this "Cheryl" girl, that she was really and truly not available at his phone number.
So he became less polite, while they kept their level of it up. They got back at him by calling more. And more. And more.
They kept leaving the number at which they wanted Cheryl--who might've changed her name, gender and ethnicity just to get away from these people-- to call. So, he put it to good use. Distributed it amongst his civil-minded friends. They got it "mistakenly" put in for other, racier, more expensive numbers in various places.
(Mulder found out about it from one of the ads he tried to call into; Langly had never had opportunity to blackmail a federal agent until then)
Within a week, the phone number was taken down.