Complex sentence: Manly the problem is when people make an overseas phone call from home, making them dial the extra "0" (for an outside line at work) and therefore accidentally contact emergency services rather that the overseas phone number.
Split into simpler sentences: Manly the problem is when people make an overseas phone call from home. Many mistaking dial the extra "0" (for an outside line at work) and therefore accidentally contact emergency services rather that the overseas phone number.