The thing is, people don't always tell the truth. There hasn't be a true documented case. If you had oral sex as your exposure then it is time for you to move on. Stop worrying and stop questioning if you got HIV from that. Adults only get HIV from unprotected vaginal or anal sex or sharing IV drug needles. Time to move on from this fear.
Perhaps this can ease your mind. Here is a study involving couples - one person had HIV and the other person did not. It is estimated that during the study period, over 19,000 instances of oral sex occurred, and none of the HIV-negative people got HIV.