Teen stealing screentime

Good Morning Nicholeen
My husband and I just started the program and have only implemented the family vision and mission statement so far. Hopefully in the future we will know how to handle situations like this, but for now we wanted to ask what to do in the meantime –
We have a blended family, my husbands daughter is 16 and has a very good handle on self government already. My son is 15 and struggles with many things, mainly self control.
His biggest hurdle is definitely electronics. We have a limit of 2 hours a day as long as grades are in good standing. He often loses his right to electronics because he:
– Goes beyond the 2 hour rule which would result in losing screentime the following day
– Sneaking to watch tv while everyone else is sleeping overnight – lost screentime for a month for that one
– Figured out how to disable the “bedtime mode” on his phone and was playing games past bedtime – this resulted in all electronics being locked away in our safe every night

In order to get his phone privileges back, we sat down and designed a screentime contract that laid out consequences. He agreed and it worked for a bit, but now we found out he was watching youtube on his school chromebook during class (he said the teacher allows that after he got his work done, however, we don’t allow Youtube and he knows that)

It just seems like no matter the consequence, it doesn’t keep him from stealing screentime.
Please help!