Two year old won't go to bed

My 2 year old screams every night at bed time! I put him in his cot and shut the door,he screams. I sit in the room with him, he screams. I take him to our room and of course he screams. And it's like a high pitched squeal and crying last night it lasted 3 hours. It's been like this for a week. I'm going insane!! He used to be such a good sleeper, I'd put him to bed and shut the door and he would go to sleep happily. Then he worked out how to climb out of his cot and he started coming into our bed through the night and waking up 4:30 onwards. One night he kept me awakw from 12:30am until 4:30am just refuses to lay down and screamed and carried on. He's not scared of the dark because we tried leaving the door open for light and he would still carry on and try to escape. What do I do? I've tried lavender bath, and oil in a diffuser and that does absolutely nothing. I'm trying anything I can think of even letting him cry it out on his own it doesn't make a difference. But he's the same with or without me in the room. I feel sorry for our neighbours honestly.