Yep, never use punishment for fear or agression. Punishing a fearful animal (most agression is due to fear) makes them more fearful, and punishing an aggressive animal who is aggressive NOT due to fear makes them angrier, thus leading to more aggression. As others have said, the corella was aggressive towards you because he was scared and was forced to bite because you ignored his body language. Now, he's too afraid to let you go anywhere near him.
My advice would be not to go near him. Before entering the room, announce your presence. While in the room, hum and sing (silence makes birds uncomfortable, since it usually means a predator is nearby). Sit a good distance away from him, and let him come to you. Animals in captivity have very little control over their lives, which makes them stressed and anxious. By letting him come to you, you've given him control over the situation which will make him calmer and increase his confidence.
When you're in the room with him, calmly look at him for a moment, then blink slowly, holding your eyes closed for a few seconds before opening them again, and repeat (depending on how comfortable he is with this, you might want to do this for less than 10 seconds). This shows him that you are calm and don't intend to cause trouble, and that you trust him (by closing your eyes for so long, you're leaving yourself vulnerable).
Basically, pretend he suffers from severe autism. No sudden movements, no sudden sounds, only make brief eye contact, don't overstimulate him, etc.
What I find really helps is reading to them. Get a children's book, sit at least 4' away from him, and read to him like you would a child (just make sure you don't scare him). I also encourage you to find out what music he likes. Play different songs for him, and see what he's interested in. If he starts bobbing his head, swaying, and "singing", odds are he enjoys the song. Try:
Stuttering by Fefe Dobson
Let the Bodies Hit the Floor
Tubthumping
Cotton Eye Joe
Lets Get it Started by the Black Eyes Peas
Everytime We Touch
Alejandro
Come With Me Now
Zombie
Mr. Taxi by Girls' Generation
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