Hi there RowanA
I trust this finds you well.
You will need to contact your current ISP to check the line number for you even if you do not have a telephone handset. Alternatively, contact Telkom on 10213 they should be able to check your line number using your physical address.
If you need further assistance please send a message to our WhatsApp helpline: https://whatsapp.afrihost.com
WhatsApp Help is available from 07h00 - 20h00 Monday - Friday & 07h00 - 18h00 Saturday - Sunday