People say these things because they are not themselves worth the benefits of the doubt from anyone. It is just best to ignore them because they don't have the maturity to change themselves,
Some people though, find it hard to discard their words and move on from it. They suffer from depression and anxiety. Just remember that life is to live for you and not to please others if they call you by names that just show their low standers and not affect you in any other way. Find some inspiration in life, there are many successful people who have been told like that they are useless but now they get appreciated by the world.