Regarding high exposure given for option trading

I am a stock market trader,I use to trade in options.

I have taken a option position on Tuesday,Total worth of 2 lakh,But I was having 1.2 lakh in my account...I have not checked it while placing the order...

I want to take option contract for my full amount..so I tried for higher quantities(as I know my broker as per exchange rule-will not give extra margin for options)and it got rejected...Slowly I reduced my quantity at some point I bought a option contract total worth of 2 lakh...(I haven't calculated at that time-Total worth of my position)....It was option position and I have holder it for 3 days...at the expiry day,My option position goes to zero-In between I have tried to square of my position,but it shows some error- where I couldn't able to square off my position.
And my stock broker also not squared off..Finally my position ends wih zero value on expiry day.

On the next day,My broker called me and said I have a debit balance of Rs.80000 to be paid..I got shocked and enquired-at last I came to know that Rs.80000 exposure was given wrongly by my stock broker for option trade.

As per NSE rule,my broker should not allow me to buy without full margin in option.

Now they are saying it is customer fault,and I have to repay the excess margin provided for trade..

I holded option contract for 3 days...in that 3 days,My broker doesn't informed me about the extra margin given....Once my option contract expired..they are informing me.. to pay that amount.

Is that legal,And now my demat account shows debit balance of 80000....

And my broker is saying legal notice will be given to repay.

I want to know,wheather I have to pay,As extra margin has been given-Against the rule of NSE.

plz advice