Need help for my 15 year old don’t know where to turn

im here because I just don’t know what to do to help my son, he was diagnosed with ASD in Feb, i was expecting this as I have a 6 year old that was diagnosed at the age of 4, anyway long story short... he has been what I think is depressed since 2016, he doesn’t move from his bedroom, he doesn’t come on family days out, I can’t get him to do anything, he attends school but I get called twice a week to bring him home because he has these random moments of bursting in to tears uncontrollably and just wants to go home. I’ve asked what sets this off and he always just replies he doesn’t know and doesn’t understand why it happens. His self asteem is on the floor, he says he is nothing, a failure, he will never be anything and he doesn’t deserve anything either. It’s heartbreaking to hear him talk this way. I have been to the gp back and forth hoping for a referral to cahms or some help but every time I get the same reply... he hasn’t tried to harm himself so doesn’t reach the threshold for a referral! So basically he has to attempt suicide or self harm to get the help! I just feel stuck and don’t know where to turn, when he got the diagnosis they said he has a high level of depression, when I asked what help is available i got told there are no provisions for teens! School said they would give him an in house counsellor.. she took him in a room with toys and played a game of jenga with him! He said he felt about 6 and she said she will check on him fortnightly, that’s it. Can anyone point me in the direction of where I can go next? I’m struggling and I just want to help him.