Calculation of tax ay 2017-18 u/s 143(1)(a)

I have submitted ITR3 for AY 2017-18 in last March .

Recently I am receiving communication u/s 143(1)(a) , demanding some additional Income TAX.

In the pdf file , what I can notice that the department is not considering 80TTA amount and that is why Tax liablity is getting increased.

I have specified total interest income in ITR , income from Other Source section ( OS) . And in ITR Chapter VI tab , I have the 80 TTA  amount ans showing properly , Although in the Calculation u/s 143(1)(a) ignoring 80TTA  amount.

Please help me understanding , Am I missing some rule here.

Thanks,

Nasipuri