As per Cenvat Credit Rules, you are eligible to take credit of the excise duty paid by you as per the invoice. When the invoice is charging 14% duty, you are eligible for that credit.
It is not the buyers work to examine the assessment done by the supplier. He has a right to assess the duty and pay duty as per his understanding of law. A buyer has no right to challenge the assessment. Thus whether hs has paid duty correctly or erroneously, it is not buyers concern. He is entitled to ake credit of the duty amount which he has paid.
This legal issue is settled in numerous judgments that buyer is entitled to credit to whatever duty he has paid, rightly or wrongly. Buyer cannot be penalised for suppliers mistake.
Take credit of 14% without any doubt.