I called it back when it called me and kept getting told to enter my voicemail access code. It ended being another number Not Mine that had  access to my voicemail code which of course also gave  them access to my voicemail. I of course changed my voicemail access code then called the number back using my old code but it already had my new one. I'm not sure what to do now since my service carrier says they cannot figure out what is happening.