Uber driver unreachable for lost wallet

Please be advised that my son is struggling to get his wallet back from his Uber driver. The Uber driver posted a pic on the app and my son confirmed it was his lost property. The next step was to contact the driver by phone, he has tried 10s of times and he cannot get through and the driver has not returned his call. We have been trying since 10am yesterday morning to resolve this. Should his wallet not be returned we will have no choice but to conclude that this is theft, as the driver confirmed on the app by posting the picture of the wallet that he is in possession of said wallet. Please advise how else we can resolve this if the driver is not reachable via the channels you have provided. I trust someone from Uber South Africa will be in contact asap.