I got half way thru your post and immediately saw a red flag. You know he didn't go to tutoring. Do not ask him how it went. When you do that you're enabling him to lie. You need to be direct and tell him you checked with the teacher. All of your communication with him needs to be calm and direct. Do not set him up to lie.
You want to teach him to tell the truth and you want to make it easy for him to tell the truth. You sound mad. Understandable. However, once you put emotion into the situation you've lost the battle. Your anger triggers his anger. Your goal is to teach honesty. Not to punish dishonesty. Punishment gets the issue of being honest side tracked into dealing with the emotion of anger.
Also the tone of your post sounds like your more focused on catching him in a lie than in helping not lie. Instead of telling him you don't trust him, try telling him that you know he will figure out a way to be trust worthy. Reward him along the way when he is telling the truth. Perhaps have her come over for a couple of hours on the weekend when he's gone the week without sneaking out. Rewards teach much better than punishment.
I suggest that you've come down too hard on him. The pressure of being punished builds up until it explodes into finding a way to relieve the pressure which results in telling another lie.
I urge you to be matter of fact. Tell him you know he lied and give him a consequence that will be over in a relatively short period of time. Give him a chance to prove that he's trustworthy. When you carry on with the consequences over a long period of time he gets discouraged. There's no way to prove he can be trusted.
It's reasonable to not let him have communication devices for a week or even two but for months? As you've learned, this did not cause the relationship to cool. It built up the intensity and the need to find a way to be together. By allowing them to talk on the phone they don't have such a strong need to be together. The phone conversations act like a pressure valve.
If he wants to make plans he doesn't need the phone, as you've seen. So not allowing him to use the phone has not stopped the behavior you want to stop.
I strongly urge you to back off some. Yes, give him a consequence for this lie. Make it quick and short. You've gone all out with the big guns already and so I'm having difficulty thinking of a good one. AV has a couple of good ideas for logical consequences.
Based only on your posts if this were me, I'd probably tell him that you know he didn't go to tutoring and ask him how he thinks he'd best learn to be honest. After a discussion during which I'd tell him I know he's capable of honesty, I'd say I'd give him another chance to start over. Then I'd plan with him what both of you need to make this work.
You've told your son in no uncertain terms that he's a liar. He's now showing you that you're right. I doubt that is what you want. Give him something positive to live up to.
Since you're the reactor and your husband is the cool one, I'd include him in this discussion. I'd talk with him first about how to handle this.
Since you're thinking that this is very serious; not just a part of your son's learning and growth, I suggest that you talk with a counselor who works with teens.
What you've done so far hasn't worked. I suggest it's time to try something different.