No feedback or assistance on where package is

I had a package mailed to my by normal mail to mail from over seas and it was delivered to south africa post office already on the 9th of June. The sender says because it was normal post the only number they have is a local post tracking number, ********** 1433. Now according to the post office they cant help me in any way at all because they say they cant work with this number So how do I get my package that is by the post office now that was sent to me?