As Mr. Rao has put, it is very difficult to prosecute the company without any proof. When you don't have any offer letter or bank statement, it is very difficult to prove that you are an employee of the firm.
If you have an official mail id and has exchange between you and your boss on any official issue, it might hold circumstantial evidence to prove that you worked in that company. (When you go for legal action, this id may be deactivated). Copy of your Attendance statement also might come in handy. All these are final options if you plan to file suit against company for non-payment of salary, and that too only if dues are above 50000. You can fight even for 5000, but anything less than 50000 is not worth fighting legally, as you will be losing hundreds of productive hours fighting the case, Add your stress as well. The best option would be to take up another job and forget this