Penalty by excise officer ?

Sir.

Mine is non-ssi unit. Last week AG audit was conducted by excise officers, in which they pointed out that i have taken excess credit of one purchase bill. Excess amount is rs. 13500. He said i need to reverse this credit & also pay penalty as per new rule. Is he right ? Am i liable to penalth ? How much interest should i pay ? Amount was for the year july 2008. I think he is referring rule 15 of ccr, 2004.

ALso, there is increase in Interest rates. Plz convey the same.