There is no such thing as a "Tax block" under the IRS rules. You may have a court order, but the IRS doesn't go by those.
You just file your return, claiming what you are entitled to. Now that you have a letter from the IRS, you provide the information they have requested to prove you are entitled to claim yourself and your child. You mother, most likely, got a similar letter from the IRS.
Usually, If someone else claimed your child inappropriately, 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 child 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 child, the next letter, from the IRS, will require you to provide proof. Be sure to reply in a timely manner.
