It's the first and foremost duty of investor to study the financial product fully and carefully before investing hard earned money. Did you go through all the terms and conditions of RD before signing the application form? Do not invest your money just because all others are investing or you're seeing lots of ads in media.
This website, like many others, gives details about almost every financial scheme present in the market with their pros and cons. Learn the art of investing.
Blaming Post office is of no use. It's India.