Interest and penalty demand

Assuming your question to be related to applicability of interest/penalty, any delayed payment of excise duty attracts interest. In this case, since you have not paid interest, SCN has been issued demanding interest and penalty. If the interest is paid within 30 days of issue of SCN, then no penalty is payable u/s 11AC (assuming it to be not due to fraud/collusion etc).

If you have taken the cenvat credit by mistake but not utilized after 1.4.2012 then no need to pay interest. The department cannot be demand the interest and penalty in this particular cenvat credit.