Senior citizen health insurance - 75 years old parent coverage

I want to buy health insurance for my mother who is 75 years old. He has high blood pressure and kidney problems. Most insurance companies are either rejecting the application or asking for very high premiums of 45000 per year for just 3 lakhs coverage. Is this normal for senior citizens? Are there any specialized senior citizen health insurance plans that are more affordable? I have checked HDFC Ergo, Niva Bupa, and Aditya Birla. HDFC Ergo is asking for medical tests before approval. Will the pre-existing diseases be covered? What is the waiting period? Please suggest the best options for insuring elderly parents.