I assume the Industrial Employment (Standing Orders) Act is applicable to you and your employer as well. In such a case, the employer is bound to issue a service certificate because of a specific provision in the Model Standing Orders. In the state of Maharashtra, the Model Standing Order No. 30 for workers and No. 28 for supervisors make it binding for an employer to issue a service certificate if it is requested by an employee. The relevant clauses are attached below. You will find similar provisions in the Model Standing Orders for the state where you were employed.
So, you should first apply for a Service Certificate from your employer and also for a salary certificate. If it is not issued within a reasonable period, you have the right to file a complaint with the Assistant Labour Commissioner of the District where you were employed. You can show the relevant provisions to the Commissioner, and he will assist you in resolving the issue.
Kind regards