Karma does exist.
there are three types of Karma:
1. instant Karma: when you do bad deeds or good deeds in this current life, you receive the fruit of it, bad or good right after that, it's easy to see
2. afterlife Karma: your bad or good deeds will have an affect in your afterlife
3. multi-afterlife Karma: in many afterlives after, you will reap the Karma that you created
the belief of Karma has to be equipped with the belief of past-life and afterlife. you should read more Buddhist texts and Sutras to understand more.
your friends and bullies that hurt you is living a good life because they have created good Karma in their past-lives
you receive bad Karma in this life and fell deep because you have created bad Karma in your past-lives.
the only way to fix this is to keep on living and create more good, positive Karma, do charity, help people, meditate, do good things, study, hold high regard to morality,... do all the best you can to create a new wave of good Karma, you will inherit sweet fruit later.