Excise

dear frnds 

here our company by mistakenly  pay excise duty 10.3% instead of 12.36% for 2 months january and february 2015

till we didnt get any notice from department

we recently observe our miastake then what is the next step to be taken

please suggest me (if we liable for interest what is the interest rate and on what amt interest to be caliculate and any penality)