Sorry to hear you are having a tough time. I hate to be the bearer of more bad news, but in my opinion, I don't think social anxiety is something that will ever go away 100% or can be "cured". However I do believe that it can be manageable, it can lessen in intensity, and we can do things to make it easier to live with.
Do you look after yourself well as in eat healthily, exercise, get enough sleep, take time out to enjoy hobbies? I think doing these are good place to start at least. These are all good for boosting mental health.
Do you have much of a support network? Family and friends who you can confide in? Sometimes when you are feeling blue just talking to somebody about how you are feeling can make all the difference. It isn't healthy to bottle everything up and to be dealing with problems all on your own.
What are your hobbies and interests? Do you do anything for yourself that you enjoy? Finding time for this sort of stuff can be a great way of forgetting about your problems and taking a break from everyday life. Try and find time every week to devote to doing something you love.
And lastly, you have to push yourself into social situations, start off by taking small steps, even if it is just a one on one thing. If someone invites you to do something, don't dwell on it, just say yes. Go for it. By constantly avoiding and turning down invitations you are feeding the beast, you are letting social anxiety win. In order for it to get easier, you have to keep fighting against those anxious thoughts that hold you back.
You can get better. It might not go away completely, but you can manage anxiety with some effort and belief in yourself. Good luck