This is a variation on a scam that has been around for a while. You receive a phone call telling you that you have been selected as the winner of a ‘cadeau’, and you need to phone a number and give a code to claim it.
The prize is a huge phone bill if you are unwary enough to actually go through with it. The number I was given is 09 80 09 04 11, but there are more in circulation, and I suspect that they change frequently given the length of the list on this site that lists surcharged numbers associated with fraud.
As always be super-suspicious of Greeks bearing gifts, or even French people (or any other nationality) promising them! If it seems to good to be true, it is in 99% of cases.
For any phone fraud, ring 0811 02 02 17