Poor mileage issue

Poor mileage. Have issues with mileage after the first service getting very less in cities like around 8-9km/h and 12-15km/h on highways. Now issues like the back side door are not locking even after locking in the remote. Ac is not that great. Corrosion-resistant fluid is leaking after a long run. Whenever goes for long drive break dust is there over the alloy wheel and it turns black. Will further update the review after 2nd service. Driven over 5000 Km as of now.