Telkom sharing personal information with questionable 'resellers'

We received a call from an operator offering an improvement on our Telkom internet connection, and who had all the details of our Telkom account, but turned out to be from 'mobile talk'. When we followed up at a Telkom office, we were told that 'mobile talk' are third party and the contract from 'mobile talk' has got nothing to do with our Telkom account. The Telkom office provided a telephone number which proved to be useless. The delivery documentation from 'mobile talk' contained NO contact details and their website (www.mobiletalk.co.za) consists of a single page with only a contact number - no business address is supp**** anywhere. Why is Telkom sharing our personal information and information relating to our services at Telkom with such a company (or any other company for that matter).