All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
If you married your paternal aunt’s daughter after divorcing her niece, who is the daughter of your paternal cousin, and her ‘Iddah, i.e. post-marriage waiting period, was over without revoking the recoverable divorce or after her death, then such a marriage is valid.
However, if you married your paternal aunt’s daughter with her niece simultaneously, or after divorcing her niece and before the end of her ‘Iddah from a recoverable divorce, then such a marriage is invalid; for it was narrated on the authority of Abu Hurayrah that the Prophet, sallallaahu ‘alayhi wa sallam, said: "A woman and her paternal aunt should not be married to the same man (at the same time); and similarly, a woman and her maternal aunt should not be married to the same man (at the same time)." [Al-Bukhari and Muslim]
Allaah Knows best.