Sa post office parcel missing

I sent a parcel about 4 month ago to London with the incorrect address so they sent it back. My parcel has been in Johannesburg for 3 months and everyday when I phone them 1 ) no one answers 2 ) if someone does answer they can barely speak English 3) they cant find my parcel anywhere in the country. I have clients breathing down my neck as I am held responsible. but got no help from my local post office , Johannesburg post office , or from the JIMC .