My last period started December 28, 2015 . I had sex with partner1 on the 8th and 9th of January, 2016. Then I had sex January15& 16th with another partner2. I took a plan B on January 17th not to get pregnant. The pill did not work. Who is the father?

I wasn't fertile on the 17th right? I am due October 3d and at another place they said I am due on October 4th.