As for their 'emergencies', tell them that for a TRUE emergency, they need to have someone from the ER call and leave a number that only ER personnel answer for you to call back to get information. Otherwise one of their friends could pretend to be someone from a hospital to try to tell you something happened. Know that ER staff won't ask for money, ever. They would only tell you that your son is there, maybe give you info if son said it was okay, maybe ask permission to do a procedure if he was unconscious and it was an emergency. They would not EVER ask for money.
Think of your phone as a door into your home. Just as I don't open the door to strangers, I don't answer the phone and open my life to strangers if I am not in the mood to do so. It drives my husband crazy, because he thinks it is somehow rude to not answer the phone, no matter what you are doing or who it is. But not everyone is welcome in my home, and I don't let just everyone in. So I simply don't answer some calls. Or I pick up the phone and put it down without answering. I especially did this with political calls.
Another response to post near the phone, one good for just about anything someone is asking/demanding, is "I don't think I would enjoy that." It is very hard to argue against, and I never say another word on the subject once I have said that. I especially like it because it tends to drive difficult people absolutely nuts. Yes, I am that person who enjoys that.
For a little while, take his photos down from your walls. Just put them all away and put something else where they used to be. When I had to make my son move out of my home I took down all photos of all of my kids. My boys look like I cloned them, so I had to take down photos of both of them, and it would be strange to have photos of my daughter up and no photos of either boy up. I put other things on the walls. It helped me not think of my son as often.
Avoid places that you went to with your son - places with good memories and places with bad ones. Purposely choose to make memories in new places. Think about things that you have always wished to do and do them.
Give back. When I am at my absolute lowest, I find a way to volunteer. Many years ago a counselor told me about the Bucket Theory. We each have a bucket inside us, and a ladle. That bucket fills up with love and we can use to ladle to give scoops of love to others or to take scoops from other people. When your bucket is low, if you lean over to get a scoop from someone else's bucket, your bucket will spill more out than you will be able to get with your ladle. If you take a scoop out of your bucket to give to someone else, you will find that your bucket ends up with more in it than it did before you took that scoop out. So by volunteering, or finding something to help someone, I end up feeling better than I did. The whole thing is counter-intuitive, but it works really well. Many thrift shops can always use someone to help sort in the back, and if you call they will let you know. Animal shelters are another place that is always happy to have someone to help.
If you are able, take a walk or find a way to move a little more. It will help you feel better. If nothing more, park near the back of the grocery store. Or stop at a park and take a 5 or 10 min walk on the way home. Or sit in that park with a book if you are unable to walk. Just spend a little time outside. If, of course, it isn't too cold where you are.
Make a favorite thing to eat or drink. Doesn't have to be alcoholic or expensive. Maybe a childhood treat. Be nice to yourself.
Each time your son or one of his sycophants tries to contact you, do something nice for yourself. Rather than giving to him, give a bit of your time to the shelter, or donate a book to a hospital library or a school library. Do something positive each time he tries to put negativity into your life and to pull the positive out of your life. He will ramp it up for a while, and then he will get the message. Let him, and esp his posse, know that you will no longer communicate with anyone but him. His girlfriend, her mother, his other friends, etc... are all just harassing you and you will call the police if they continue to contact you. If your son is truly hurt seriously, the hospital can contact you directly. His girlfriend does not need to EVER contact you.
If girlfriend keeps calling, or her mom does, get a self defense whistle () and blow it each time you hear her voice or her moms. Or any of their posse's other than your son's voice. This might be easier than dealing with the police, depending on your local police and your prior dealing with them.
If they show up at your home, don't open the door. If your son has a key, change the locks. Make sure the windows are all locked and have pins or dowels preventing them from opening. Tell him it is a bad time and he needs to call before he comes over. If he does not call he cannot come over. Tell him that his girlfriend and the rest of his posse is not welcome on your property at any time, ever. Call 911 if he gets verbally abusive or won't leave or tries to break in. Press charges.
I know it is hard to press charges against your child. I had to do it. It is the ONLY way he will believe you are serious this time. It is also the ONLY way the police will know you are serious. Otherwise they might not respond and you might need them. I am so sorry it has come to this.
I hope one or some of these are helpful.