Hi. Nosipho - this is common sady. What you can do is to:
1. Get another SIM card that has enough airtime (R3 or so) or data bundles (3MB or so)
2. Insert it in your phone ans insert your phone and insert your original SIM card in another phone and turn both phones on
3. Open the Whatsapp messenger app again and attempt to activate (yes type your original cell number in the supplied field to verify it
4. Wait petiently for the minutes count down (you should receive an SMS on the other phone that has your SIM card ) - open that SMS so you can access the 6 degit code when needed
5. After the count down there should be a field where you are to type the verification code - type that code and proceed to verify then number and follow the on-screen instruction to complete your Whatsapp setup process.
Please comment below using the comment button if further assistance be necessary.