Cannot handle my aussie

I've got 12 week aussie for 3 weeks now. Its been up and down, I've sunk deep into regrets just to enjoy him the next day.

But I have so many problems with him that I'm constantly asking myself if I should return him to the breeder.

He's overstimulating super quickly. He will turn into a demon in seconds on a potty break or during play. If he's going for a "2" he'll overstimulate every time.

And once he's activated I cannot handle him, I'm a big guy and he's overwhelming me physically. He'll go for my legs, trousers, jacket or boots and start to bite and pull, if he's latched on I cannot correct him in any way. And I did try multiple things. I tried pinning him to the floor or grabbing him by his loose skin and correcting that way, but it doesn't do anything, if released he'll bite again. I tried redirecting with a toy – no bueno. I tried restraining biting with a leash, he'll continue even if he starts choking himself.

I consulted a trainer about this behavior and they said that he has too much stimulation and I should make wake cycles shorter. At this point he's waking up, going potty, having a sip and going back to crate. This worked for a while but now he's refusing to fall asleep.

During one of my walks I actually broke his finger when opening a door, so its now double to the problem. He cannot do physical activities, he cannot really walk because his bandage is getting wet and really he's getting more and more irritated rather than getting better with time.

On top of that I cannot motivate him with food – he'll go for it, but reluctantly – on all training videos I've seen puppies are over-exited to get a treat, in my case he'll do the thing I asked him for, and when presented with a reward sometimes even refuse it.

I tried sniff mats or puzzle toys – he'll flip them over (and then ignore the treats inside)

In summary:

– I get bitten, a lot, with very little inhibition progressing

– I get "herded" on walks

– Food is only mild motivator, play or even pooping overstimulates him quickly

– Any ways I know that should let him vent are not working – either ignored or cannot be performed due to injury

– All my day is spent by preventing him from injuring himself even more / wrecking havoc in home (will actively try to escape play pen, bark and jump) or nip at everything

– I work from home and I cannot find any time / mental capacity to do so (I've taken 2 first weeks off too).

I don't know what to do.

I fear that even if I invest time and effort now, for next couple of week, he'll continue being awful.

I don't know if I can continue, give up on him and return to the breeder or put him through training camp.