How To Go For Medical Negligence Case In The Absence Of Post Mortem

In March 2018 my sister had her appendix removed through laparoscopic surgery but after 2-3 days she was again admitted to the same hospital because of severe pain in the abdomen region. She underwent open surgery and on 20th March 2018 she passed away. We were not in our senses that time as it was a huge loss (she was just 27 years old) so we couldn't demand post mortem. I am confident that the surgeon has made a mistake. It can be anything from not removing the complete appendix to not completely suturing that area to damaging the intestine during first laparoscopic surgery and many more. The hospital hasn't provided us medical records even after asking multiple times. We made a complaint to the civil surgeon but he gave that surgeon and the hospital clean chit, we made a complaint in the CM helpline but till date no solution. We filled a case in consumer court but our advocate just gives us dates but we aren't called for any hearing. Please advise what can we do.