Can a offer be treated as appointment letter ?

I had joined a company 3 months back. There I had signed the offer letter that was previously mailed to me. After joining I did not get an appointment or joining letter even after asking verbally. Even there were no pay slips. I found major problem with the company and process management of the company as there was none. There were no training or knowledge transfer. I got a new job and I left the company with a resignation letter and without serving the notice period. I worked there for 1 month. After that I was demanded of different amount of money in different mails from the company head. Now I have received an advocate notice stating I have to pay 1lakh as per the "appointment letter". In some places he has mentioned "the offer / appointment letter signed by me". So I need to know that if the offer letter can be treated as appointment letter? And what should I do next.
Thanks you

Dear Meet,
Have you read the offer letter do they had a clause of paying rs. 1 lac. please tell what was written.

What was the understanding of the offer letter. Did you notice at that time, any clauses which are against your thinking ? If you had accepted the offer letter, that means you were agreeing to all the terms of the offer. Now, I dont think something can be done, unless it is against any laws of the land and you can take legal recourse to.
Best wishes