I feel your pain, and have been there...
I agree it is better now to choose one brand or mix and stick to that(*), same with type of teat now. And also get the temperature consistent, lukewarm is better than too warm or too cold if they are fussy.
If you tube, tube only barely enough to keep him alive each time, not a full feed. You need him hungry going into each feed.
Does he drink water? If so, remove it for a while, he may be filling up on water.
Flow can be as important as teat type - too fast and it can go down the wrong way, so they fight against the teat; too slow and they give up trying. So start with a new teat and a small hole, then gradually increase the size of the hole. You do need to increase the flow as they get the hang of it and suck harder and harder.
You sound very experienced at bottle feeding, so this bit is more for others reading this post who haven't done as much as you have... You need to ensure that the bottle is able to "unvac" itself, or it gets harder and harder to get the milk out against the developing vacuum. The little Pritchard teats (yellow cap, red teat, fit on a 500ml Coke bottle, other fizzy drinks are available) have a wee hole next to where the teat comes out from the cap, that needs to be uppermost so the bottle can draw air in. The "non-vac" teats also have a hole in the rim of the teat, so again, make sure that is uppermost as you present the bottle to the lamb.
Finally, don't underestimate the power of mother love.
I had a lamb giving me similar heartache and one feed, I decided that instead of the thrice-daily fight, I would just cuddle it, and not worry about a feed. After a few minutes of cuddling in, the little mouth started questing under my ear, I slowly brought the teat up to my hairline... That time I got more milk in my hair and down my neck than in the lamb, but every feed after that, I cuddled it until it started to quest, and then it would feed.
(*) Although there is an argument for giving him 2 days on electrolytes, to get him fit and feeding first. He may now have formed a bad association with milk, which you will need to overcome.