This usually happens when you receive a phone call from someone claiming that they are from a fraud prevention division of a well-known long distance carrier or from a calling card company. During the call, the scammer informs you that there has been activity on your calling card that appears to be suspicious. They will be asking for the last eight or nine digits of your calling card They tell you that it is in order to verify that this potential fraud is being charged to your calling card.
The scammer will tell you the first five or six digits of your calling card to get your trust, asking you to follow up with the remainder. These first five to six digits of calling cards are fairly common. Never, under any circumstances should you give your calling card number to anyone over the phone. This is not how a real long distance carrier would verify this issue with you. If you have given out your calling card number, immediately cancel the card and request a new one.
Click here on how to file a complaint.