Based on your posts, it could seem like your income or employment is not legit. Not sure how your employer accounts for your salary paid as cash in the company accounts especially as there are no records for it.
Your salary must have increased year-on-year, isn't it? Is it still paid as cash (after demonetization)? And, is it still below taxable limits?
Even if your income is below the taxable limits, it is advisable to file 'Nil returns' as this helps to prove you have genuinely earned income (for a visa application) + for claiming any other benefits.
Your employer must provide a letter + other conclusive evidence to prove your salary was paid as cash since 2012. For example, did you sign cash receipts for the cash salary each month? Did you deposit the amounts each month in your bank account? Does your employment letter state you will be paid as cash? Profession Tax records of the employer to prove you are an employee? And, if I'm not mistaken, as a salaried employee whose salary is below taxable limits, you are entitled to government medical benefits, right? Do you have evidence to prove this point?