When did Silvia Duran deny the person was Oswald? Not once to my knowledge. Certainly not in her testimony. She testified that when she saw Oswald's picture in the newspaper the next day after the assassination, she told her husband this:
CORNWELL - Okay. Did you have any other discussion that you can recall with him [i.e., her husband] about it? based on that news report? About your contact?
TIRADO/DURAN - With my husband?
CORNWELL - Yes.
TIRADO/DURAN - I only told him, I think this man came to the Embassy.
CORNWELL - Then, the next morning you saw a newspaper.
TIRADO/DURAN - Yes.
CORNWELL - Were you sure at that time that that was the man?
TIRADO/DURAN - Yes.
Later:
TIRADO/DURAN - I show the paper to Horatio [her husband] and told him this is the man that went to the Embassy and I went to the Consulate and I look in the Archivos and I saw the application, I saw that it was the man and I went to the Embassy and I talked to the Ambassador and I told him that this...
Yes, her description of Oswald is off - she believed he was older, for example. But she has never, to my knowledge, denied that the person was Oswald. If someone has evidence she has, please provide it.
And Alfredo Mirabal, who was also in the consulate at the time, testified that the man was Oswald.
Duran's full testimony is here:
http://mcadams.posc.mu.edu/russ/m_j_russ/hscadurn.htm