Package not received from Ladvia that was already send 23/12/17

Good day. I bought a electrical part for my vehicle on 16/12/17 and it left Ladvia according to the tracking number RS ********** 78LV on 23/12/17, when I phone EMS postal service days goes by that no one answers the phone and when they do answer the phone they say that it did not arrive yet. How can it be? How do I go about for them to search for my package?