Please don’t put yourself down for withdrawing when you were young. It sounds to me like you were shy and socially awkward from a young age. It’s sad you didn’t get the help you needed then but it isn’t your fault. Also sad is that you were bullied for something you couldn’t help and didn’t know how to fix.
But that was then. This is now. Unlike then, you have the ability to get yourself the help you need. It sounds to me like you are in a vicious cycle: You are afraid to participate is social situations so you withdraw. Isolating prevents you from getting any practice with the social rituals so you become less confident to try. Being less confident, you withdraw some more and feel bad about yourself. Clearly, this cycle isn’t getting you anywhere.
I strongly urge you to find a therapist who specializes in social anxiety. Ideally the same therapist will be running some group therapy. Group therapy can give you needed practice within a safe environment.
You said you got some CBT (Cognitive Behavior Therapy). That’s a great start but, since you are still feeling distressed, it was only a start. Ask that therapist how you can access more long term treatment and support with the added service of group treatment.
Do follow through. You need and deserve to have a life that includes comfortable interaction with others.
I wish you well.