Wrong assessment yr in itr

I am a first time tax payer. I put the wrong assessment year in filing ITR for AY 2014-15 (FY 2013-14). I put 2013-14 as AY instead of 2014-15. Now there are some calculation form IT dep that I should pay instead of getting the refund I am entitlted to. becuase they are calculating tax for FY 2012-13 when I did not pay any tax. ( started wroking from May-13). Only today I got the reply from IT dep. What can I do to rectify?

Thanks & regards

Swagat