Idea Cellular — gst on june bill

Address:

Kolhapur, Maharashtra, 416101

My bill due date is june 12 2017 to 11 july 2017
But they charge tax on total bill
How can they
Gst applicable from july 1 2017

I call customer care near about 1hour but they are busy
No one can answer me
How they apply gst to total bill it is against the rule and regulations