To not be able to discipline DS12

[Needl]

Please help,I need advice. Huge backstory, so please bear with, I'M NOT A TROLL.My DS12 is getting out of control. He got in with a really bad group of older girls at school last year, and even though we have moved him to a different school, he continues to keep in contact with these girls online. He is not allowed social media due to being underage, so he went behind our back and set up an Instagram account to keep in touch with them. I monitor his internet use, but its been a hectic week, so I didn't find till this weekend. What I found shocked me, these girls have been sending him porn and encouraging him to go through mine and DH's personal things when he's home alone and report back to them with what he's found. When we confronted DS he went apeshit, screaming that we were intrusive and over controlling and shit parents. He even pulled out his pocket knife and waved it around threateningly. Dh grabbed the knife and DS ran out of the house. DH went looking for him, but he ran off everytime Dh got close. In the end we had to call the police to pick him up and bring him home. We asked the police what to do, and he just shrugged and said he's probably embarrassed but don't worry he will grow out of it.
The next day we sat Ds down and said that there would be no more smart phone or internet access, and he was grounded for a month. He responded by hurling his skateboard at my head. Which we have now confiscated. The day after that he accompanied me on a walk to the shops and while I was paying, took off again. I gound him at park with a local boy (who is a good kid), borrowing his phone. I went over and said "sorry x, ds is grounded and can't play right now ,you can have your phone back, ds is coming home ". Ds just smirked and handed the phone back, said goodbye to his friend and came home in a good mood. Later that night I checked his Instagram and saw he had used that time at the park to contact one of the girls, asking her to delete the messages and he'd be in touch later.

I'm at a complete loss, how do I enforce consequences, when its just a game to him? He shot up over lockdown and is bigger than me now, and seems to think he can do as he pleases. I've made an appointment for us to see a counsellor later in the week. Has anyone else had a teenage son who has behaved like this?

The things that concern me are:
He has a knife aged 12
He's being violent in the house
He's being sent porn by older girls
One of the girls is known to be vulnerable and has a history of sexual abuse
Vulnerable teens are often groomed by gangs and older criminals
Teenagers are often used to recruit other teenagers for older criminals
His obsession with getting to a phone to message them is worrying

Have you been through his belongings and is there a chance he has a cheap pay as you go phone that he thinks you don't know about? I'd be concerned that he's on the fringes of child criminal exploitation or county lines, or he's not involved but from what you've said he's an ideal candidate to target.

Pornography is not benign it actually affects children's brain chemistry that's why it's so damaging it's to do with the affects dopamine has on a undeveloped mind

From what you're saying you've discovered the tip of the ice berg counselling may help but you need to be honest with the counsellor about his level of exposure and the possible grooming activity that's gone on

There is support out there specifically for this please access it.