is there a difference between 投诉 and 抱怨? All I know is that they both mean "complain".
投诉=complain (to a department)
抱怨=grumble (usually talking to a friend)
If you look at the character, 诉=suit, 怨=grudge
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.
抱怨 is to complain 投诉 is to lodge a complaint
投诉 means to complain in the legal or "formal" sense.抱怨 means to complain in the social sense.
They both meant to "complain," just in different contexts.
投诉 is to express your discontentment to some organizations or institutes; 抱怨 is usually used to grumble to people around you.