I worked in a school 6 years ago. Salary was paid in cash and we signed a register while getting salary. No other payslips, paystubs provided. No income tax as the job was in saudi. Now i need that experience to show 3 years. However, the school is not ready to provide me with anything as i left long ago. I dont have even a single proof of salary. They are not providing a copy of that signed register. They are not providing reference letter. I am getting reference letter from ex colleague who will mention that my salary was paid in cash. What are the other ways to convince visa officer?