What's the ruling on eating after Fajr (when fasting) because the Azan was late?

In my country, the Fajr Azan is around an hour after Fajr comes except in Ramadan. While I was fasting in Shawwal and I forgot that they give the Azan late, I (most likely) drank at Fajr time because I didn't hear the Azan. Does this affect the fast or not? Note the fasting was voluntary