No, the demand is not correct. It should be for 1 month only. Read section...
[(1A) Without prejudice to the provisions of sub-section (1), if any such person, principal officer or company as is referred to in that sub-section does not deduct the whole or any part of the tax or after deducting fails to pay the tax as required by or under this Act, he or it shall be liable to pay simple interest,—
(ii) at one and one-half per cent for every month or part of a month on the amount of such tax from the date on which such tax was deducted to the date on which such tax is actually paid, and such interest shall be paid before furnishing the statement in accordance with the provisions of sub-section (3) of section 200:]
According to me you should pay interest only for 1 month and you should write a letter to dept. attaching challan that "We have made interest payment for only 1 month according to the provisions of section 201(1A)(ii)"