Paying 2 months for no service rendered

Bonitas deducted R 7336 from my monthly salary. When i called the call centre I was told that I short paid Bonitas from March and April for my adult dependent which is not true. My adult dependent was only recently added 5 May 2015 after i sent an an email 14 April 2015 asking how come my adult dependent cannot be added. <br> <br> Why must i pay R3750 for March and April if she was only added May 2015. My adult dependent could not make use of Bonitas services March and April now I must play this is unacceptable<br> Reference number 230515Q9PY4F<br> I want an explanation