Phone your network provider and inform them of your loss:

Cell C: 140 from Cell C numbers or 084-140 from other cellphone networks.

MTN: 173 (pre-paid) or 808 (contract) from MTN numbers or 083-1-173 from a landline or other cellphone networks.

Vodacom: 111 from a Vodacom number or 082-111 from a landline.