About PPF Account

I opened a PPF account 2 years ago at a Post Office. I made payments in it for 2 years for tax saving purpose under Section 80 G. This year I didn't pay into my PPF account as I didn't have any taxable income. But I did go to check my account balance and was surprised to know I have to pay a penalty of Fifty rupees for defaulting on my payment this year. Turns out every year we have to make a minimum deposit of Five Hundred Rupees into our account else will be charged. Okay, why do I always have to learn things the hard way?