It is the mistake made by the organization which accepted the resignation and relieved the employee concerned by not documenting the fact in its own internal records. Therefore, there is no dual employment in fact but for the omission in the records of the previous organization. Besides, payment of salary and statutory deductions there of would have been made only for the period of service rendered by the employee in the organization only.
Thus the only option to remedy the situation is correcting the records of the poster's organization accordingly. 5th October 2019 From India, Salem