Incorrect demand notice, how do i file rectification

Hi, I had filed income tax for AY 2013-14 online, painstakingly making sure that every entry is matched with Form 26AS. For my AY 2013-14, incometaxefiling.gov site also shows "Tax credit claimed is fully matched with tax credit in 26AS"

I have, however, now received a demand notice of Rs 1280 instead of a refund of Rs 1320. The TDS calculated on the return is lower than the actual TDS deduced by Rs 2600/-.

I am surprised that IT return TDS computed by CPC mismatches with my form 26AS total. How do I rectify this online when no changes are needed except that they need to calculate my TDS amount as per 26AS.

Regards

Anirban