Mobile phone

[belay]

Ds isn't allowed his phone in his room at night but every once in a while he has a wobble and argues . Tonight he said it wasn't fair that I have my phone. I explained that the care home need to be able to ring anytime about 90 year old grandma but he just didn't want to listen. He stormed off to his room with his phone and starts texting me. Saying he wanted to check something on Minecraft and needed access to Google. I logged in to his Google account and hey ho some very unsuitable images . His phone is filtered by Sky broadband buddy and the also the Safe Lagoon app. So I reckon he's got the pictures via Bluetooth ?
Obviously he was desperate to be alone and look and the pictures !
But he's lied and defied us.
I'm stuck what to do next ?

For what I've seen the parental control apps are not infallible, some inappropriate image can still be found online, so I think he found it on some website. Is it an android device? Knowing you will check his web activities should be an effective deterrent for him. Is it the first time happening that? Maybe he expected you will never find out, so let him be aware you will check his online activities and actually do it every few days (also log in your son google account and go to myactivity.google.com/myactivity).
Another option could be he bypassed/turned off the parental control app or he used another browser/app to navigate online, or he used chrome with incognito mode (that sometime goes without filters) or vpn connection. I'm not so tech savvy but these are the common ways teen bypass parental control. I don't know the parental control you are using, I use Google Family Link and it forces chrome in safe mode and disables incognito mode. So to do next is installing also Family Link to prevent that, it's very safe and works properly to filter contents, except for the screen time limit that is too easy to bypass (so maybe it is worth keeping the others parental controls too). Then to prevent vpn connection or using other browser be sure any new app installation need your approval in advance, set chrome as default browser, block any other app that let browsing websites, and, very important, block access to the phone setting because they can change everything by there (if there isn't the option to block the phone setting in the app lock list on your parental controls, as there isn't in Family Link, use another app, look for "app lock" in playstore, we use LOCKit).
Then limit the screen time, less time means also less possibilities to see inappropriate stuff and like to make a habit of looking only to useful things. Consider experts recommend only 2 hours a day of maximum screen time for teens 12 to 18yo, including any screen, tv, pc, game console, phones... even setting the limit of 1 hour a day for the phone could be the most appropriate thing.

How old is he, I think that makes a big difference. Teens seem to be very adept at bypassing controls if they want to: the most important thing is to have a dialogue

Let him be. He’s a teenage boy. Stuff on his computer, almost every teenage boy will have that. From the way he had to ask for access just to google, it seems you should give him more respect and let him have more room to do what he wants online.

Perhaps look at extending bedtime hours, or turning off wifi and data so he can have his phone for necessary calls, like you. Then you’re both in the same boat?