The Greek number: +302106261000
French number: (+33) 170 031323

If you are a gold member there is also a special number available, which will put you to the head of the CS queue. You can find that after logging in at the website.

You should be able to cancel your check in online. If you really cannot get a hold of anybody you can then use the website (manage my booking) to see if that gives any options regarding cancelation or moving the flights. Have you booked a Light or Flex fare?