Experience Certificate From Ex-employer 10 Years Back

Hello Members,

I am a software developer having 10 years of experience in IT industry. During my start of the career i joined a small company and worked there for 1 year, when i left the company i did not get relieving letter so my exit was not clean from that company, conditions they put me for getting my relieving letter were nearly impossible to fulfill, and my new company did not required any letter so i joined new company.
After 9 years in different companies with proper certificates i need to apply for immigration to Australia for which I need to show 10 years of experience, and for this I need to get 1 year of experience letter from my ex-employer.

I need your help in below areas -

I called them up and asked for letter, they gave very casual type of answer and said they will look into it but it may take time and since a long period of time has passed (10years), they may not able to provide the letter.
1. I have sent them a mail having my joining letter and salary slips, what can I do if they refuse the letter?
2. What if they refuse letter by saying that my exit was not clean, should I try to negotiate with them by asking to pay my last one month salary (at that time it was Rs 15,000) as my dues?

PS:- I have the signed photocopy of my offer letter which in addition to other conditions also mention this clause - "My engagement will be liable to be terminated on one-month notice by either party"

Thanks!!!

Senior members, could you please provide your valuable inputs?
Also can anyone help let me know if I posted this thread in wrong section?
Thanks in Advance

10 years is a long time and I don't think a company is liable to keep records of employees for ten years. Practically it will be very difficult to find your records (until they keep it and digitalized it). I do not think you are legally entitled to ask for relieving letter after such long delay of 10 years. If you say you are now willing to pay Rs.15,000/- as notice pay as your exit was not proper, then they might ask you to pay the interest for 10 years. So it is better not to agree to pay anything on paper.
Write a simple and polite letter stating your date of appointment as well as resignation annexing their with copies of appointment letter and resignation letter asking them to send a relieving/ experience letter. Send it through registered post.
However, can you not show your experience by way of producing appointment and resignation letter for the said period of 1 year?

In my considered opinion, that in the given facts, the copy of the Offer letter, by itself, would be a substantial document.