You should have given resignation at least. Now question arises how much money you may be required to pay. Under West Bengal Shops and establishment Act, by which you seem to be governed, one month's notice or wages in lieu has to be paid by employer if the employee has rendered one year service. Otherwise the employer need not pay. But if you are governed by ID Act then after 240 days service workman has to be given one month's notice. Thus before one year no liability to pay notice period accrues on the part of employer in WB. On the same parity liability of employee has to be understood otherwise contract will be violative of section 23 of the Contract Act. Any contract contrary to statutory provision is void to that extent. Pl see the recent thread in this regard. Since the employer has demanded Rs.65000 from you to give you relieving letter, it means he has not contemplated any disciplinary action against you for absconding. You have rendered 3 months service out of which he has paid you 2 months wages. You send a reply giving resignation and stating that there is no liability on your part to pay notice period under WB shops and establishment Act. Instead the employer has to pay you one month's salary unpaid by it. If you want you can surrender your unpaid salary and ask for relieving and experience letter.
Thanks
Sushil