They called using another number 704-815-0158 then called back on this number 704-443-2515 trying to reach an individual who use to work at our company.  They've been told not to continue to call under any other number of disguise.

busy when called back unknown caller only phone number shows

Left a message saying it's very important that I call back, but when you do it's a weird busy signal or it don't do anything

This nuber comes up initially as unknown but calls my cell phone three times a week between 8 - 9 AM.  I picked up once only to be told to call a different number.  Scam!