How much percentile do I need to score in the CAT 2020 to get a call from IIM Ahmedabad as a general category candidate with 65% in 10th class 70% in 12th class 81% in engineering?

This might be disheartening but the truth is you will never receive a call from IIM Ahmedabad even if you score 100 percentile. 

• According to the latest selection criteria of IIM Ahmedabad, you are disqualified even before appearing for the CAT exam. Since you have a poor academic record, your chances of getting a call from any of the BLACKI IIMs is almost none. 
• Sohum Sen, who was one of the toppers of CAT 2019 did not receive a call from IIM Ahmedabad with a 99.98 percentile solely because of his academic performance which is 81% in 10th; 72% in 12th, and 7.93 in graduation.
• IIM Ahmedabad considers giving a call to candidates who have a minimum of 80% in their 10th and 12th examinations. Sohum Sen failed this criterion and you also do not qualify considering this fact.

Other top institutions give less importance to past academic records, you can aim for them. 99.7+ in CAT and 99.5+ in CAT XAT will ensure high chances of your selection in such institutions i.e. FMS, MDI, XLRI.