Ramadan begins with the sighting of the new crescent and ends with the sighting of Shawwal's crescent, as Allah says, "So whoever sights the month, let him fast it" (Quran 2:185). The Prophet ﷺ said, "Fast when you see it and break your fast when you see it, and if it is obscured from you, then complete thirty days of Sha'ban." Thus if the crescent is not confirmed, the month of Sha'ban is completed as thirty days rather than relying on doubt. Scholars differ over whether one global sighting binds all lands or each region follows its own sighting, and both views are held by respected imams.
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.