On line self assement tax chalan mismatch correction

For Assessment year 2013-14 i paid self assessment tax though online banking ,but commited mistake .
In place of Assessment year 2013-14 i mentioned year as 2012-13 in the challan.After this i submitted the return with required ref numbers etc.
The mistake remained un surfaced till now,but now i have received a demand note from IT dept for the amount.
How can i settle the issue,Is it possible by calling through help line,Can i send a mail (If yes to whom?),