I received a call from a number +0.

I received a call from a number with only "+0." My sister answered, and on the line, a woman who knew my first and last name asked to speak to me, but I wasn't available. My sister asked who she was, and she replied that she was my career advisor, even though I don't have a career advisor, and she said she would call me back during the day. What is this strange number? I also received a call yesterday from a number "033," but I didn't answer.