Green ring neck Parrot biting

So i bought 2 ring neck green parrot their age were about 20 days, since then i fed them and everything, it’s been 4 months one of the parrot died and i am left with only one now. At first he never attacked me and when i called him he always replied back. The problem started when i had to leave my house for 20 days and i had to leave my parrot with my aunt and uncle. When i came back he had already learned whistling which my aunt said that uncle trained him to do that. When i brought him home again he is now biting everything including my hand and is scared of everything, he was replying to me at my uncles house but not anymore, he is always quite and scared. What should i do please help ( it’s been over 1 week since he is acting like that). How much longer do i have to wait for him to act normally.