Those
Hello.
Those past social experiences were terrible, and I'm sorry it happened. We can look at it as something that didn't happen 'to' you, but happened 'for' you. In other words, if you look at it as victim mentality, you will definitely feel like you cannot experience anything other than harsh treatment by people in society.
First, a little reality check. Our current western society is horrendously 'me' and 'image' focused. In some circumstances, yes, this will work if you alter the way you look, how you talk, and how you approach people, but ultimately it's about you being genuine and comfortable with yourself even if you screw up. You are going to falter for a little while as you engage again with socializing. That's expected, given that you probably are fixating on bad memories.
What I would do, is start small. I'd volunteer somewhere, where you're giving your time to help others in need. Food banks, hospitals, charities. Once a week. This type of social experience will habituate you to think about other people, and not focus on yourself, especially when you're helping the disadvantaged. Volunteer work can also be a safe place to practice basic social skills.
Choose your social platforms wisely at first. You're starting out fresh, and you want the best chance of success. But start small. I'd also keep a written journal and write down all the positive social experiences, not just the negatives.