Note: If your parents are separated or divorced and there is a dispute between your parents over who should have claimed you as a dependent, only your mother can address this. She would file an amended return for the years in question and claim you as a dependent (even if someone else already claimed you for that year) which might result in additional tax credits or other benefits. Then, the IRS will send letters to both parents asking for more information to investigate who should get the credits, based on the rules, the facts of your case, and who has the better proof. If your mother is awarded the dependent benefits, the other person who claimed you will receive a bill for repayment of excess refund, with interest and possibly a penalty. But the process will probably take 1-2 years at this point.
The rules for claiming dependents are here, including the special rules for children of divorced or separated parents.
https://www.irs.gov/pub/irs-pdf/p501.pdf
