why does "cb" in text only have 4 numbers?

I get a weird cb notification when receiving text messages from one person.... a cb number that is 0000000**** and the ****will be 4 numbers. But if I try to call back I get a "call could not go through" message.

I do not get this all the time from this person, just once in awhile and they are in my contacts.

Not sure, offhand. Have you tried calling your carrier to see if it may be a network issue on either their end or the contact?