Gangar Eyenation — Product default and charging extra money

I have been making specs from Gangar Eyenation (Mulund) from 2011. Every time I bring my own frame to make specs. I have really high power, and hence, for better quality I have been trusting Ganger Eyenation for so many years. Even they are aware about this. This time, after 2022 I went to prepare new specs as my number was slightly changed with a change in the angle. And below is what the series of events taken place:

Every time, I put glasses which cost me around 7-8K. This time, I wanted to make two specs, one for my daily use and another as a spare one. So for the daily use, this time I had put glasses which cost me around 12k. And for the spare one I made it as my usual one in the range of 7-8k. For this decision, the staff tried convincing me to put the glasses of 12k in both specs. I was giving them logical reasoning, stating that’s really not needed since these are my extra one. But they tried convincing me. I didn’t budge. I was firm on my decision and I told them to proceed as I instructed. They gave me 10% discount on each one, and my bill amount came to INR 18,[protected] + 7380). For which they sent me a soft copy on my WhatsApp. They asked me to pay 50% advance, and then as a round figure they took 10k from me.
After 2 days, I got a call from them saying, there is crack to my frame and I need to buy a new one. Otherwise, if they proceed and anything happens to the frame in 2-3 months, then that would be my responsibility. I asked them to share photo with me. And in photo, it was quite evident that the crack was not there earlier, and it has happened only because of staff negligence for which they were asking me to pay and asking me to buy a new frame.
Since I was tied up in my office schedule, I asked them to hand over me my extra specs and told them in 2 days (probably by Sunday) I shall be coming to buy new frame, just give me my extra frame now, because it is causing me real inconvenience while working on laptop. They said okay, we can hand over. But you pay the balance amount. I asked them, I have already paid 10k and adjust the cost in it. Anyway I will need to make another specs since lenses are ready. The staff was so stubborn, they were not even ready to do that, they asked me to pay the full amount. I was telling them, I their customer since last 10-12 years, still they did not even consider once. So basically they asked me to pay INR[protected] + 50% of 12300). I was requesting them to adjust it in whatever advance I have paid which was anyway more than 50% I had paid (ideally I was supposed to pay only INR 9222, but I had paid 10k). At the time of taking payment, they did not consider that I’m paying extra. And when I had asked them to adjust, them came up with the rules saying you will need to pay. I told them, I’m only entitled to pay an extra INR 2915 since on the invoice the amount given was INR 11070 which was after discount, for this they told me discount we will give you later. And they forced me to pay without discount 50% advance. I should have paid only INR 2140 (since in advance 10k I had paid INR 775 extra and with discount I was entitled to pay INR 2915 which amounts to INR 2140), they took INR 3380 from me, without any discount even though on the invoice discount amount was clearly mentioned. So they took extra INR 1240 from me out of nothing ! Which I was only supposed to pay once I get my another frame back. But they forced me to pay.
They did not take any signed declaration from me stating that the ownership for their negligence will lie with me, and they did not even take my signature on the invoice, they did not have any valid proof.
They only have intentions of looting people, and mean only business. No consideration for customer, only mean money, charge premium costs, and for their negligence they charge you without having any valid documentation signed.