Vodafone — vodafone sim outgoing call validity period

Address:

711302

I am receiving sms in my phones which are not having unlimited recharge plan that every 28 days I must recharge with rs 35 min to make outgoing calls even if my balance is there much enough to do call. When I called customer care of Vodafone they informed me it is directive made by Trai. I read reports actually this is the way these companies are trying to increase ARPU of their customer base. But its clear cheating as one have enough balance to make calls. How this can be a valid step?