Central Board Of Secondary Education [CBSE] — School did not follow the cbse guideline in tabulating grade 12 result

This is regarding the class 12 result of my son. We strongly believe that the school (Ekya school, ITPL, Bangalore) did not follow the board guidelines in tabulating the grade 12 result. They have given marks randomly to their preferred students and since my son did his X from IGCSE board, they completely ignored his class X marks in tabulating the class 12 marks. Now when we are asking them to show the calculation they are asking us to go for improvement exam. I don't understand why a child should be put into trouble for the mistake of a school. As the cbse board normally has the facility of revaluation and showing the papers if the candidate is not satisfied this year also we need such facility. During the rise of third wave of the covid why only few students have to write the physical exam even though the board has put lot of effort and the schools can't follow the rules and guidelines and want to take their grudges on some particular student ?