National Highways Authority Of India [NHAI] — Minimum balance in fastag not justified

Dear Sir, I have a Fastag for my vehicle with a balance of 69 rupees. I need to pay 40 rupees for my Toll, but my vehicle gets blacklisted. On enquiring I am told that I need to keep balance of 200 in my account.
I need to know the following
1) Why should I keep my excess money with Fastag when I have sufficient amount balance to pay the toll?
2) By keeping this excess money, will I get the interest on that money as per market rates?
3) Why this compulsion of keeping excess money in my Fastag, when I do not need to use it. I hardly use my vehicle to go out station where I need to pay Toll.
4) Who is benefitting from the interest incurred on the excess money of individual who has kept his hard earned money in Fastag?