Tata Consultancy Services — HR asking me to put resignation

After completing my graduation, I worked in startup company. I worked there for 1 year 6months. Later, I got selected with TCS as a Business Associate. At a certain time, I got a job with TCS as a permanent employee With 3years of experience.
I was happy as it was a dream come true for me to become a permanent employee in TCS. I accepted the offer letter and was asked to submit the documents online. I was asked to join as early as possible. So, I shortened my notice with the previous employer and releived as early as possible.
My first employer was a startup company and from my previous company was their and previous company HR replied properly to the BGC team about my employment. I was informed that, since the company was their, the BGC team could not prepare a proper report and made my offer status negative.But they said that offer letter and relieving letter is not considered as a proof and they required only bank statement . I got my salary from my first employer as cash in hand for first few months and remaining months bank statement was provided already but they need all months bank statement. I even explained them that. But they insisted me for bank statement for the Cash on Hand salary. I do have deposited that money in my bank account but they didn't consider that.
I made them understand that I was a ex-TCSer as I worked in TCS as a BA for 1yr and 3months and I have provided all the necessary details of my first employer when joining TCS as a BA. I also informed them that I will provide them with my Manager, Program HR, colleagues and my previous TCS BA employment records for proof. But the answer I got from them was, the BGC conducted by TCS BA is different from the BGC which TCS permanent role conduct.My onboarding process was done already and I got the Offer letter from TCS.And now I am jobless.
As they requested the more clarification about my previous employment .I told them if they want any additional proof about my previous employment I can collect and ready to submit .But the HR refused and she is asking on the bank statement for the complete working years .I do have submitted the bank statement which I have with me .But still she wants to see things via online verification.
If someone from TCS management team had a chance to see this, please respond back. If required, I can provide the details if I do have someone to help me get my TCS offer back.