Kindly refer to the following link(s):
Ruling on eating while the Azaan is going on during Suhoor (Sehri,pre-dawn meal)?
When fasting if Fajr athan has started can I eat & drink or must I stop immediately
Is it permissible to eat suhoor while athan is going on, if you wake up late?
The true Fajr (break of dawn) and mistakes in some timetables
When should I stop eating and drinking when Fasting - at the 1st or the 2nd Athan?
Accurate time for starting and break of fast ( Umm Al Qura Timetable)
In Suhoor I drank a few sips of tea after I heard the Athan, is my fast valid?