You say that you have served notice period as per the conditions of employment (presumably as mentioned in the appointment letter). You had been accommodative of your employer's requirement and you even arranged your replacement also. Against this backdrop, what average employee could have done?
Now I recommend you visiting your past employer personally and request them to provide the Service-cum-Employment Letter (experience letter). If possible also ask for "No Due Certificate". If they do not provide you with this letter then you may approach the Labour Officer (LO) of your area. However, whether you are eligible to approach LO depends on your designation and whether you had any subordinates.
Without being releieved from your Employment, again by issue of a Wriiten Order/Acceptance and a Discharge from Muster-Roll Paper put through, it was unwiseto Join another Establishment and the Second Esta erred in allowing you to Resume Duties without submisssion of Written Releiveing/Termination-from-Employment Letter.
You please persuade the Employer to accept your Resignation and approve the same. Double Employment is Prohibited and liable to Punishment.
My previous employer is well aware of that and hence they are not accepting the resignations.
So that the employees will get in trouble. I have worked with the organisation as HR for 11 months and no single employee has left on a good note. Even when employees served proper notice there payments were delayed unnecessarily. Not only that, if company get any mail for background verification of an employee, they would never reply with honesty.
Company is also into lot of fraudulent activities and making false promises to employees.