POSTNET lost or stole parcel (****med)

My sister sent a parcel from POSTNET THOHOYANDOU on 02 August 2023, paid for courier + insurance =R142 to POSTNET SERENGETI in Kempton Park, till today 08 August 2023 the parcel have not arrived and when we track the Waybill no. it just shows like the parcel arrived in Johannesburg on 04th August but after that nothing or anyone has bothered to make sure that it gets to intended POSTNET Shop. Surprisingly is that on the courier they wrote "delivery 2-3 working days" but on our side is over 4 days without our parcel now. I tried several times to call their call centre number ***8 and no one answers, just rings till it gives message that is not available (what kind of call centre is this)