Not provided with Salary specified in Offer Letter

I was working in a IT startup X, first as an intern for 6 months and then full time for 4 months(monthly salary of ₹20,000). The start up X has a sister startup Y(had common directors). I was actually working on a product which was under the name of Y. I initially wasn't aware of it. I got to know about it, when I was told to put Y's name on one of the product's screen. I was offered full time in startup Y in October 2019 for ₹30,000 monthly salary. There were talks about the product being acquired by a company Z. But then we were told that Y would be acquired by Z and we would be working for Z. I don't exactly remember during which month was it told. Y credited full amount for first 2 months, but during these two months I was asked to pay back ₹10,000 for each month to one of the director. As far as I can remember he said we would get the money back. The next 5 months I was credited only ₹20,000. I hadn't questioned back then. On May 2020, we started working for Z. I was offered 4 months of probation for ₹25,000 and after that ₹30,000. After probation, Z said that due the pandemic I would not be given ₹30,000 till February 2021. I was given ₹25,000 for following months. On December 2020, I decided to quit Z. Before I quit, I sent a mail to directors of Y about my pending payments, where I received ₹20,000 instead of ₹30,000. I had also attached the offer letter, salary slips that stated ₹30,000 and bank statement that showed ₹20,000. I was told to get on a call to discuss the matter. In the call, I was told that such an arrangement was discussed with me when the offer was made. They said that it was mutually decided that the salary on paper would be ₹30,000 but will be paid ₹20,000. They said it was done so that I could get ₹30,000 in Z .I don't remember such a statement being made. Also I remember one of my colleague was also expecting the full amount. So I believe I cannot be wrong. To sum up, I was denied ₹70,000 over a span of 7 months. I regret not being on top of the matter during the initial days. Any advice would be appreciated. Can I claim the money legally?