son (16Yrs) bought moped without permission

[hateironing]

What should I do? He hasn't received a license, completed the course or have insurance and I think he's riding it as it's no longer in the garage. Should I call the police? He is not listening to us.

Goodness.... there’s clearly a massive backstory here. How horribly worrying for you at the moment. Is he answering his phone, any idea where he is? Around here youths on mopeds are often associated with criminal/drug dealing networks. How does he have the money to buy a moped himself?

I know it’s MN cliché but perhaps you could call 101.... you don’t have to give your details straight away but perhaps they could advise what action they would potentially be able to take if you did formally report? I might be worried however that he’d be more likely to have an accident trying to evade police than whatever he’s doing now.

What age is he?

I'm sure you have already explained that if gets caught doing it illegally then it will mean even longer before he legally gets his license - might make him think it's worth the wait.
As soon as he is 16 with his provisional license, insurance & CBT he can go.
In the meantime if he persists, I would probably find a way of removing the keys.