It's got to be the most frustrating.
One thing I would say is to be sure to do a thorough self examination on the issue of lying for the adults in the home. Kids are terribly alert and will pick up on the smallest trend and run with it. So if any adults have been in the habit of telling any lies at all, the kids have noticed. Things like "we can't come tonight, we have a commitment" (when you really don't and you just don't want to go and the kids know it) or "I don't have any money" (when they know you do but you just don't want to spend it on that
). To kids there is not a big difference, so if the grown ups have used any lies over the years, it may be time to do a family re-commitment to truth telling, even when it is difficult. If the whole family is going to work on it, it will be easier for your son to come along. "I know I lied to your teacher that time when you weren't really sick but I'm going to commit myself to only telling the truth from this day on."
So I"m not blaming you for this, it's just a thing to pay attention to and one that sometimes parents don't "see" for themselves, because the kids were in on the lie
and therefore shouldn't have picked it up and thought they could do it too.
Aside from that, be careful that you know for certain that something is real before accusing him of lying. Then don't let steam come out of your ears. You could try simply saying "when you're ready" to tell us what really happened, that is when "X" privilege will resume. And go about your business. Simply remove whatever privilege is most fitting--natural consequences are best, so something related to the problem at hand, or an electronic device if that would be more powerful. But consequences cannot be given if anyone in the home is still getting away with lying, even on little teeny weeny items.
This is an important one to nail. When he is a teenager, you need to be able to trust what he is telling you.