Shazz that is such b#ll shat the way your DS has been treated. WTF is with calling on saturday afternoon?? It should have been dealt with immediately. Have they got written witness statements from everyone involved?? What has happened to the other boys? I would be making an appointment to see the principal ASAP, if all the "witnesses" were friends or victims of the bullies then they will not have got the full story. Did they talk to all the kids individually???
Sorry to go on but this really upsets me, I do not think the school has handled it well at all.
Much love to you babe sounds rough atm.