All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Initially, the fasting person should abstain from all things that break the fast. So, if the person is knowledgeable in the matters related to distinguishing dawn from night, then he can rely on his own knowledge regardless of when the Muath-thin (i.e. the person who calls the Athaan) calls the Fajr Athaan. But if he is not knowledgeable in such matters then he should follow the Muath-thin completely and abstain from all things that break the fast, as soon as he hears the Athaan, especially if this Muath-thin is known not to call Athaan before Fajr time as some Muath-thins may do (i.e. call the Fajr Athaan before dawn). Now if the person eats or drinks after the appearance of dawn, then he has first to complete the fasting of that day in respect for the month of Ramadan and then make up that day by fasting an additional day. But, he does not have to pay any expiation (Kaffaarah).
Allah knows best.