The meaning of „Mhmm“ isn’t understood

This week I have said „Mhmm“ about seven times to different people, but every time the reaction has been the same. People think I haven’t heard the sentence and repeat it.

Actually I heard it perfectly. And I tried to tell them that I got the message.

The same has been happening with the word: „Ahaa“. When I’ve said that, it also brings up the same reactions. People repeat themselves. Even when I only wanted to be encouraging, saying: „Ahaa, I get it, please go on.“