The rent increase is exceeding the rental index. What to do?

Good day everyone!

I am looking for some advice.

We are renting a bedroom hall for 40000. Our contract will end in November. He sent us a notice informing us that he will increase it to 50000. I have asked them to lower it. He made it 48k increase, but he is increasing over the rental index.

As per Land Department, the rental index is 6k. If I file a case against him, is there any chance that I could win the case? And how much do I need to pay in filing a case?

Thank you in advance!