Europcar discount

I hired a car last month from Europcar with my Discovery card and according to the information on Discovery website, I qualify for a 10% flat discount if I didn't have a pre-booking online.

I never got that 10% from Europcar since they said it will come from Discovery themselves.

1 month later, I never saw any cashback concerning that transaction.

So today I decide to call to inquire about it, I keep on being redirected between departments.

Can someone assist please