Stuck payment

The fee of Rs500/notice is reasonable.

However to satisfy yourself you may inquire at your location.

What was the notice period stated in standing orders applicable to the establishment (certified/Model) and extended to the designation of employee

Don't look into appointment letter alone. The notice period in standing orders shall prevail upon appointment letter.

The lawful authorities are:

Inspector under Payment of Wages Act (applicable to all employees drawing wages as per def. of wages in the Act up to Rs.180000/pm). You can file complaint within one year from due date of payment of wages. IN case of separation the wages should be paid by last day in office or within next 3 days or max. by usual pay day. Demand FNF statement in original for verification and acceptance.

Inspector under Shops and Commercial Establishments Act (if it is commercial establishment and employee is covered as 'Émployee'  as in this Act)

o/o Labor Commissioner If employee is covered as ''Workman" as in ID Act

Your lawyer can ask you a set of structured questions and  can opine you would be covered as Employee/Workman or not.

Or you may have to approach Civil Court 

Please follow the advise of Mr. Kumar Doab in this regard.