Poor petrol quality poured in my car

Good day I had a bad horrible experience with Caltex garage Olifantsnek, they poured a poor petrol in my car which I got last year 2020 still brand new, we poured the petrol about 1300 or 1500 my car started to fail, I did take it up with them which VW did drain the petrol out and cleaned the petrol tank they did pay the 6000 however VW did not their job proper now the car is stuck messed up due to the poor petrol quality they poured and to fix the car it needs about +18k. Now they refusing to fix my car. Please help