Unjustified premium increase

I was e-mailed regarding premium increases for 2 of my dependents that only joined my schemefrom the 1st October and are ironically still on a waiting period till the end of December. I emailed the call centre and received a call from a gentleman who proceeded to explain that this was Discovery's standard annual increase. When I explained that I was unhappy with this since I had only just added on my 2 dependents the only response he could give was the generic 'this is standard practice' I was then put through to the manager Liska who explained how the increase is calculated.I am still however dissatisfied with the response I have received. No one can explain how an increase like this can be justified for 2 people that have just joined the scheme. This is unacceptable and I require a proper and reasonable explanation or else I will consider my options and take the matter further. I will await for a response on e-mail.