Itr for assessment year 2015-16 not filed

Sir, I could not filed ITR for the ssessment Year 2015-16. Now i received a letter from the income taxdepartment to comply with stating that transactions are showing in form 26AS. THAT RELATE TO MY SALARY AS EMPLOYEE FOR THE PREVIOUS YEAR AND THE TAX IS DUE TO ME. NOW I WANT FILE ITR..HOW I CAN I FILE NOW. I TRIED ONLINE BUT IT COULD NOT SUBMITTED.IT SAYS THAT THE TIME IS OVER. PLEASE SUGGEST A WAY TO RESOLVE THE PROBLEM. I DEPOSITED DUE TAX BY CHALLAN AND NOW THERE IS NO LIABILITY OF TAX.