There could be a mistake---or maybe someone else accidentally (or deliberately) used your SSN on a tax return. Whatever the reason....when this occurs---the only way your parents can file their tax return that claims you now is by mail. They need to print, sign, and mail their tax return.
And although you are sure you answered the questions correctly --- look carefully at your own 1040 and see if the box is checked for being claimed as a dependent. It is up near the top of the form near the words Standard Deduction.