rude agent at springs mall

i was at a mtn store in springs mall, and their agent who's supposed to be patient with me and answer all the questions i had was very rude - his last straw was when he raised his voice at me. i would like to lodge a formal complaint against him but this is far as i go because mtn aren't answering my calls. if you have any idea on where i should go to lodge a complaint, please let me know.