You can't dispute it and you can't amend it. You can only file a competing tax return. The IRS will straighten it out*.
You may have to wait a year for your stimulus payment. When you file your 2020 return in 2021, you will have the opportunity to report the amount of the stimulus check(s) you did receive, and if it was less (including not getting any) than what you were entitled to, you will receive a credit on your 2020 tax return.
*If someone else claimed you, as a dependent, inappropriately, and if they file first, your return will be rejected if e-filed. You would then need to file a return on paper, claiming yourself, if appropriate. The IRS will process your return and send you your refund, in the normal time. Shortly (up to a year) thereafter, you’ll receive a letter from the IRS, stating that your exemption was claimed on another return. It will tell you that if you made a mistake to file an amended return and if you didn't make a mistake to do nothing. The other party will get the same letter you did. If one of you doesn't file an amended return, unclaiming the exemption, the next letter, from the IRS, will require you to provide proof. Be sure to reply in a timely manner.
Winner gets the tax benefits; loser gets to pay the IRS back with penalties and interest.
See full dependent rules at: https://turbotax.intuit.com/tax-tools/tax-tips/Family/Rules-for-Claiming-a-Dependent-on-Your-Tax-Ret...
