When I was 7 working on math homework, my genius father was trying to help and he ended up getting mad and telling me I was too stupid to learn.

That was it. I graduated high school and couldn't even multiply.

In my 20's I started teaching myself math and slowly gained confidence.
Today my job is to work with millions of dollars of other peoples money. I am very good at what I do.

I use that one example for myself as a reminder that I do not have to follow my father's prediction. Or anyone else's either.

Use positive self talk to try to turn it around. Search for examples where you have accomplished something you are proud of and keep those close as reminders.
Very hard work to undo the words of our parents, just keep putting in a new CD to listen to instead of that old record album.