He denied the marriage contract then affirmed it; does that count as a talaaq (divorce)?

Such a question cannot be answered without knowing the exact words uttered
by the husband or knowing what he intended and meant by those words – did he
intend by denying it to set himself free from his wife, because he was upset
at their spreading the news of the marriage? Or did he simply wants to
conceal the marriage without any intention of setting himself free from his
wife? 

If he simply wanted to conceal his marriage, without any intention of
divorce, then that does not count as a divorce 

The fuqaha’ (may Allah have mercy on them) discussed a similar issue. They
said: if a man is asked, “Do you have a wife?” and he replies “No,” but he
is lying, that does not count as a divorce. 

Ibn Qudaamah (may Allah have mercy on him) said: If it is said to him, “Do
you have a wife?” and he says, “No,” intending to lie, that does not imply
anything… because saying “I did not have a wife” could be a metaphor (for
divorce) if he had the intention of divorce. If he intended to tell a lie,
then he did not intend to divorce her and it does not count as such.

End quote from al-Mughni, 7/400 

Al-Bahooti (may Allah have mercy on him) said: If it is said to him, “Do you
have a wife?” and he says, “No,” intending to lie, he has not divorced her,
because it may be a metaphor (for divorce), and if he intended to tell a lie
and did not intend to divorce (then it does not count as divorce).

End quote from Kashshaaf al-Qinaa‘, 5/247 

Therefore if this man said, “So and so is not my wife,” if what he intended
by that was divorce, then it counts as such, but if he intended to conceal
the marriage, then it does not count as a divorce. 

If he denied the marriage, such as if he said, “I did not marry So and so”
or “I did not do the marriage contract with So and so,” this wording is to
be regarded as a lie, and it does not count as a divorce. 

And Allah knows best.