Oh OP this sounds so hard but your OP about calling social services made me lol because I totally empathise. My two are a year younger but there are similarities - arguing about attending school, going out in middle of the night, money, cooking food at night, waking me up... Your OP made me lol - calling social services and saying please take them lol! Their friends being lovely and always round here, me working my arse off.
It's far from over for us but what has appeared to help a little - even if it's just my sanity:
Setting curfews - they don't always abide, but say 10pm, then they'll come in at 11...
Letting some things slide as long as they are safe - telling them that - I'm glad you're ok
Expecting no thanks for some things, asking for a thank you for lifts, extra money, even if it's grunted at you
Calling their friends to make a nuisance of myself if they don't come in - I did this a bit as someone's on here suggested it - saved this for if they were out in middle of night. When they complain remind them they simply need to let you know where they are
Trying to repair the relationship with the older one, even if it means giving up on expectations. This relates to attendance. Just asking him what's happening. I'm not perfect at this - still get really frustrated when he's being a lazy so and so, but his attendance has improved a bit. He's also got a goal for a very practical sixth form course, not academic at all - he can't bear classroom work even though he's definitely not stupid.
Read Get Out of my life but first take me and Alex into town. I found this super helpful.
Also reverse psychology
Also getting them to work for their money - this is a mixed bag - not always a very good job!
Getting a WiFi controller on the router. This has been mixed. Older one actually took the router and ran away once in protest when it was really bad. But we negotiated red lines as it were - no WiFi at night - and sometimes I have had to give in and just say, well it's your life. Sometimes I turn it off and I hear them move lol - if I want them to clean up - then put it back on
I get head of year (male) to talk to him quite a bit as I acknowledge with school that I'm his mum and he just can't seem to listen to me sometimes.
Planting the seed that once 18 they're either working or in full time education or I'm not paying for their phone!
Far from perfect!!
Super hard. You have my deepest sympathies!