How to gain self confidence?

I have extremely low self confidence, I have been made fun of about my looks for a really long time I remember a kid came up to me and said what's wrong with your face? it looks off idk no one wanted me to sit by them in the lunch room so I pretty much hid in the bathroom until lunch was over and not only that girls would reject me like it was a game even though I never said anything to them all the friends I had turned on me and even the teachers kind of gave up on me saying that I was a drug user(which I am not and I have never done drugs) and a loser pretty much and I am also shy and quiet so before class there were times where people would come up to my desk and just try and get me to talk like they didn't like me or want to talk to me they just treated me like a freak and people still sometimes do that not only that I never really had friends I had acquaintances people who would say hi to me in the hallways but nothing else and even people that say are my friend never really talk to me don't really return texts and when we do make plans they always forget or have something come at the very last second and really only talk to me when they want me to do something for them or want me to help them through something plus a lot of people in school for the longest time thought I was stupid also my parents don't really much either I mean sure they encourage me with music or art but that is it they treat me like a child when I am in fact 20 they have always had a knack for just pointing out my flaws that I was already aware of and felt bad about I also overheard my mom saying how I am going to end up being a drug dealer she has called me emotionally disturbed and my dad when we used to really fight he would say things like " go to hell " or calling me " hateful ", " evil " even " spawn of the devil " they tell me all the time how I have no life even when they talk with relatives on the phone they talk about my brother but with me " oh, he's good " that is all they can say about me hell, people even criticize me over having low self confidence like I chose to be insecure I went on a date with this girl and I stepped out of my comfort zone a lot I asked her out and during the date I was myself and things seemed to be going really well and we texted a little bit after that and I asked her out again and she yes she stood me up I drove an hour and a half out of my way I waited four hours(a little long I know) and I texted her and she said she had work but she gets off at 5:30 and it was 8:00 she didn't even bother to text me and I asked if she wanted to reschedule and said we'll see and then a day later she said I was too insecure and a loser but we only had one date she never really got to me or give me a chance and this is the way everybody around me is and has been since I could remember I mean I do have good friends that I can talk about anything and have things I am good at like drawing,guitar and song writing but I still can't shake this low self confidence what should I do?