Hello
Inform Zazoo Limited (formally know as Net Mobile Solutions) via their Facebook page here https://www.facebook.com/net1mobilesolutions.co.za and they should be able to assist you with the de-registration process. You can alternatively contact them using any of the below contact details if you do not have a Facebook account.
Phone: +27 11 463 7233
Fax: +27 11 463 5158
Email: info@zazooltd.com