breaking fast before sunset

Q: If a person thought the athaan went off while fasting in Ramadhaan (he heard the athaan on the radio or someone gave the athaan as a prank) and he broke his fast is the fast valid?

Q: Someone is doing kafaarah for ramadan fast. She is on her fifteenth fast. However when she was on her fifth fast she had broken her fast two minutes before iftaari but she carried on doing her kafaarah. What is the conclusion? Will her kafaraah start again from after that day or does she completely have to start all over again?