As far as I know:
1. to have it cancelled: yes; to have the miles recredited: no (if you have booked the "Meilenversicherung"/miles insurance, you would get your miles back course)
2. yes, but the new flight date must be within 365 days after your first booking. And you have to pay EUR 50,-.
3. UK: no; contact number +49 30 3434 3433 is located in Germany.