Application declined. No reason given

I'm an existing Telkom customer, I have new 24 month data contract which is a few months old. I recently app**** online for a R279/month phone contract on Black Friday promo. The response from Telkom \Unfortunately your application has been declined during our initial pre-vetting stage". That reason is not clear and it's only Telkom which seems to have issues with my applications. Other credit providers don't have problems with me. I'm perfectly aware that my credit score is very good. It would be better if Telkom could be clearer so that I can correct my application in case I missed something on the application"""