Is it ok to drink orange juice ( or other citric fruits juice) right after kickboxing ?

Sometimes citric acid can burn if you have it on an empty stomach, which might be why you felt the burning sensation, but it wont do you any harm if you drink it after a workout in general. In terms of eating dinner that late, it isn't really good for the digestive system to eat so late and it is not conducive to a good nights sleep either. You should try having a protein shake after the workout (try a whey isolate) as this will nourish and fill you up, but wont lie on your tummy all night or disturb your sleep.