I got FASTAG through PayTM on Dec 15. I was told that all I need to do is to maintain a minimum of Rs150 balance in my Paytm wallet and that is sufficient for the FASTAG to work, but everytime I go through Toll plaza it says negative balance in my account and I have to pay cash. I have called Paytm nearly 40 times on their 1800 number an no one picks up. Their customer service really sucks.