Insurance: Can Insurers remove critical features like Reset or remove SI slabs from their policy?

Hello,

My parents have held a health insurance policy since 2007 from ICICI Lombard of Rs 2 lakh each. The policy came with reset benefit. However in 2021 policy document the company removed reset benefit for SI of less than Rs 2 lakh. No prior information was provided. When we complained in 2023 policy year they removed the SI slab of Rs 2 lakh and moved us to Rs 3 lakh slab. By doing so the premium increased 66 percent, from Rs 42k to 70k. For my dad who is 80 plus it increased 75 percent to Rs 1 lakh pa. We asked the insurer to retain the same SI but the company said that Rs 2 lakh slab doesn't exist anymore so it's not possible. My parents can't afford such high premium and will have to opt out of their policies. They can't even port as my mom is a cancer survivor and sad has a weak heart. Does regulations allow insurers to do such things unilaterally without customer consent?