Mumbai Customs — custom duty charged incorrectly for used electric guitar by mumbai customs

Address:

Mumbai, Mumbai City, Maharashtra, 411011

My dad who lives in japan has sent me electric guitar through speed post as a gift to me. The unit was held at mumbai customs for 3 days, i had called them for the reason, they told me that send us an email saying it a gift from dad and including consignment number and aadhaar copy for identity proof, the adviser didn't tell me anything about custom duty fee. Today i received a call from local post office in pune (Delivery location) saying that i have to pay 10500 inr as custom fee. I was shocked to hear that as the evaluation of the unit is itself 19600 inr so the custom duty is more than 50% of the actual product price.
Mr avedesh meena (Examiner inspector of mumbai customs) has wrongly charged me starting from the actual price of the product in inr.
I understand and ready to pay the custom duty as per correct cth code for the unit which falls under 92079000 category and as per calculator the fee is approx 6000 inr. 10500 is not acceptable.
Requesting you to do the needful.
Attaching the necessary pics including the custom letter and calculator image