We went through similar with ds (Yr 2), earlier this year. I found it exhausting and draining and was amazed there wasn't more support - either through health or education services.
Like yours, ds's school told us he was fine once he was there (but he would explode at me as soon as I picked him up). Forcing him - on the advice of the school - made everything worse, his anxiety levels went through the roof, he was refusing to go to bed, staying awake until midnight, began refusing to leave the house at all, etc etc
If I could go through those months again, I wouldn't force him in (but I didn't have to to work so I can see your situation is really different). I would also have asserted myself sooner and more strongly at school and pushed for some action from them.
In the end, we felt we moved him to a very small, very nurturing independent school. I never thought for one minute that I would end up paying for my child's education but we'd reached a situation where we felt there was no choice. And fortunately he is happy there and we've had absolutely no school refusal since he started in Sept.
It has shown me how much difference the right environment can make. I hope you have more success than we did in finding the right setting in the state system.