I hadn't seen this until now.
You took out insurance for loss of earnings.
You did not lose any earnings.
You made a claim in error.
They paid you in error.
You received €10,000 which you should not have received.
You should pay it back.
People and companies make mistakes all the time. People should not benefit from mistakes.
The next question is whether you should have been sold this policy in the first place. If you were sold a policy on which you could never have claimed because your employer gives you sick pay, then you should get those premiums back.
Brendan