Dear Piyali,
As resignation of job is a voluntary act of the concerned employee, so he/she has the right to withdraw it before it is accepted by the employer. Since you are in notice period, your resignation is a prospective one and as such even the acceptance of it by the employer before the expiry of the date specified in the letter of resignation can not affect your right to withdraw it before the specified date. A resignation tendered to take effect from a future date will be inchoate state until the specified date expires. As per the ratio decidendi of the judgment of the hon'ble High Court of Karnataka in Kushalnagar Works, Kudige v P.Nagaraju [ 1988 I LLN 1019], refusal of the employer to permit withdrawal of resignation is unjustified and on withdrawal of resignation, the employee continues to be in service.
However, to avoid unnecessary conflict in this regard send copies of your withdrawal to your immediate boss and the HR department as suggested by Ashutosh..