Teenage son difficulties

[chrisski33]

Hi
I'm having difficulties with son who has just turned 15.
His mum (my ex-wife) committed suicide last year and although son seems to be coping I'm not getting much respect it honesty from him. He has two younger siblings who are my biological kids but 15yr old is from another relationship of his mum's but I adopted him when he was 2. He is coming up to do his prelims (mocks) but has shown no signs of revision but claims he does revise but happens to be when I'm not in house! He quit a paper round he had in morning saying it was tiring him out at school and not helping but I suspect he might have been sacked from the paper round. Despite making sure he's in bed promptly he stays awake til 11. He spends time playing games in the pc and Xbox and doesn't have screen time after agreeing with school counsellor that should try not having screen time. He finds the idea of screen time and WiFi curfew controlling and seems to think any rules are unfair.
I'm finding the relationship tricky as he's not listening and is always being a smartarse which really gets my back up. Any ideas on how to deal with it? How do I get him to study and not lie about doing it when hasn't?

Very true @Pinkbonbon!
We had a good Christmas and new year and son had a good 15th birthday in december.
Have decided after discussing with family and from advice from here and others to let him organise his own revising however there isnt any evidence of him doing so. We we will see how he gets on in his prelims(scottish form of mocks) Im fully aware the studying at 10.30pm on his phone was just a ploy to use his phone.
His life seems to be xbox and silly memes on Instagram some have been inappropriate others fine but he has different sense of humour to me.
Probably main thing ive done recently is to walk away rather than rise to the argumentitive responses he gives. It has been mentioned by other adults he needs to speak better towards others esp adults. He has a good relationship with my mum which helps.
Thanks for folks suggestions has been helpful. Hope you all had a good Christmas and New year

I was a difficult little bastard as a teen (not saying your son is BTW) and when I look back it defo wasn't anything my parents did.

I was unhappy at school, started smoking loads of weed, then harder drugs by late teens. I eventually sorted it out and have a good career in a technical skill and a good relationship with my parents.