Law does not work on emotions. Big companies have money and manpower to drag a litigant till Supreme Court and there is technically no 'illegality' in doing so. This is the unfortunate truth.
Whether the company is registered under Shops & Establishment Act is also immaterial in your case of termination.
If the company is really coverable under the ESI, PF and Minimum Wages, then you may lodge a complaint before their respective authorities so that you can pressurize the company. Again this has nothing to do with your termination case.
You may get any due salary, leave encashment, gratuity, retrenchment compensation etc.