Please Help: Rectification of tax credit mismatch between assesee and computed under section 154

I had filed returns online for AY 2012-13 during last year. After assessment I received demand of Rs.3230 under sec 143(1). As per my returns prepaid taxes taxes of return and tax as per 26AS are matching. However the tax on bank interest paid by me as advance tax amounting Rs. 3234 which also reflected in 26AS statement still IT department demanding Rs. 3230 which I have already paid under advance tax. Then I had filed rectification under sec. 154 under "Tax credit Mismatch" Under the catagory tax payer is correcting data for tax credit mismatch. But after rectification still they are demanding the tax which is already paid and which is also in 26AS. Please tell me whether my reason for rectification was not correct or under which head I have to file rectification or whether tax on bank interest paid by me under Advance tax was wrong hence assessment is not getting clear. Pl. help me.