Way back in 1994 I collected my youngest son from primary school and he told me he was not going to school again!
Of course I took him back as usual the next morning, had a word with the Head, who said who said he'd have a word with his class teacher to see what was wrong.
Well, four years on from that date he was still not in full school attendance. We tried changing schools, which didn't work, so we voluntarily went for home schooling.
I think the home tutor came for an hour a day.
At weekends he played golf and went out with his friends so he was still socialising.
He did return to senior school prior to exams and from there went to do a sports course at our local college.
Then started labouring for a local builder, who encouraged him to do Maths evening class, then he did a bricklaying apprenticeship.
At age 43 he now runs his own local building company and can also be seen on DIY SOS as part of the build team:-)
Coincidentally another lad who lived near us was a school refuser as well and he now runs a local rendering firm.
Having a child refuse school is mega stressful and I found it very isolating as well.
My advice would be as follows:
Contact the charity Education Otherwise.
Always think of your son in Positive terms, tell yourself there will be a good outcome! Believe me, it certainly helped us.
If he leaves with zero qualifications he can still learn and progress.
Do not go down the route of it must be Mental Health problems.
I used to remember the words of Churchill: Never, Never, never give up!
Good luck to you and your son::-)