Before you have standing to sue your ex wife for misrepresentation and damages you will need to prove and have a court declare that you are not the father.
In Texas you would normally have 4 years after the birth to contest, this is based on my assumption that the child was born during the marriage and you are the "presumed father". But the 4 years deadline goes away if you presumed you were the father based on misrepresentation. Here is the law:
§ 160.607. Time Limitation: Child Having Presumed Father
(a) Except as otherwise provided by Subsection (b), a proceeding brought by a presumed father, the mother
, or another individual to adjudicate the parentage
of a child having a presumed father shall be commenced not later than the fourth anniversary of the date of the birth of the child.
(b) A proceeding seeking to adjudicate the parentage of a child having a presumed father may be maintained at any time if the court determines that:
(1) the presumed father and the mother of the child did not live together or engage in sexual intercourse with each other during the probable time of conception; or
(2) the presumed father was precluded from commencing a proceeding to adjudicate the parentage of the child before the expiration of the time prescribed by Subsection (a) because of the mistaken belief that he was the child's biological father based on misrepresentations that led him to that conclusion.
Here is the definition of "Presumed father"
§ 160.204. Presumption Of Paternity
(a) A man is presumed to be the father of a child if:
(1) he is married to the mother of the child and the child is born during the marriage;
(2) he is married to the mother of the child and the child is born before the 301st day after the date the marriage is terminated by death, annulment, declaration of invalidity, or divorce;
(3) he married the mother of the child before the birth of the child in apparent compliance with law, even if the attempted marriage is or could be declared invalid, and the child is born during the invalid marriage or before the 301st day after the date the marriage is terminated by death, annulment, declaration of invalidity, or divorce;
(4) he married the mother of the child after the birth of the child in apparent compliance with law, regardless of whether the marriage is or could be declared invalid, he voluntarily asserted his paternity of the child, and:
(A) the assertion is in a record filed with the bureau of vital statistics;
(B) he is voluntarily named as the child's father on the child's birth certificate; or
(C) he promised in a record to support the child as his own; or
(5) during the first two years of the child's life, he continuously resided in the household in which the child resided and he represented to others that the child was his own.
(b) A presumption of paternity established under this section may be rebutted only by:
(1) an adjudication under Subchapter G;
Note, the reference to Subchapter G is referring to the first statute cited above, § 160.607, is contained in Subpart G.
Let me know your follow up questions.