Idea Cellular — Secondary balance crediting by Idea cellular

I had topped up the credit for 35 Rs along with the validity of 28 days, however amount has been credited as secondary balance.
As i did not know what is the secondary balance i checked the internet and came to know that this balance was to be used within a specified time period,
Which is unacceptable.

i tried to send a message from my mobile as currently i am out of India and after sending a message it is seen that the amount was used from the main balance.

I don't understand why the secondary balance amount which is to be used within a month was not debited.
Also why is this amount being credited as secondary balance??