is there a difference between 投诉 and 抱怨? All I know is that they both mean "complain".
It's right that they both mean complain, and that is because "complain" has different meanings. If you look up complain in a dictionary , 抱怨 is corresponding to the
1.To express feelings of pain, dissatisfaction, or resentment.
and 投诉 is corresponding to
2.To make a formal accusation or bring a formal charge.