Ok, Stands, you slipped. It is normal and natural. It was a $10 slip - not the end of the world. Chalk it up to learning and go on. TRY not to do it again.
When he keeps calling and bothering you - block his number. You can call customer service at your home and cell phone co and they will teach you how to block a number. You can unblock it later when you are feeling stronger. It is NOT a permanent cut off, just a way to give you a break. The repeated calling is HARRASSMENT. he does it because he thinks it will give him what he wants.
If you make it so he can't call you for a few hours, or even a day or 3, it is not the end of the world. You can call and check in with him when you feel stronger.
Just because you have a phone does NOT mean that you are obligated to speak to anyone who wants to talk to you anytime they want your attention. You have the right to not take any call you don't want to take - for ANY reason. You don't even have to give the reason. Tell him you are in heavy traffic, taking a bubble bath, getting a massage, screaming into a pillow, or tell him nothing at all.
As for the car, is he forcing his way into the car and refusing to get out? Drive to the police station or call 911. That is NOT safe and is something that can end up with someone HURT. You will need to tell 911 that your drug addicted son will not get out of your car and is pressuring you for $$ or a place to stay or whatever. Tell them that you are afraid to leave him alone in the car because he may damage it or steal it (both could happen. he may even have keys to the car taken while he lived with you or visited you - I know several addicts who have done this. They have taken keys from anyone's car/home they could get their hands on. Then if left alone in the car they drive off with it. They say that it was "loaned" to them and they have a key to prove it!!! So don't leave him alone in the car.)
A restraining order is an option if he refuses to follow your requests regarding contact. If he comes into your home and refuses to leave you have a real problem. In some areas if you let him stay even ONE night he can them claim that he has tenant's rights and you would have to formally evict him. Not in every area, but another member had this problem at one time.
If you get a restraining order be SURE to talk to your daughter and other son about it. You want to give them the info AND let them know you will support them if they choose to do this also.
You have made some great progress in breaking the codependent and enabling cycle with difficult child. I know he is trying harder than ever to control you, to keep you in that enabling pattern, but you are really starting to think things through and act purposefully - rather than just reacting to difficult child's behavior. You should be proud of yourself, it has been a real struggle for you.
What ever you do, be sure you have your cell phone in your pocket. Especially around the house where you get comfortable but he may show up and refuse to leave. You need to practice excusing yourself to the bathroom in a way that will not make him suspicious. Then you can phone 911 or husband for assistance.
Remember - Progress, not Perfection. You are doing a great job!