Operators are - in the case of a financial compensation - free to determine the way in which they grant the compensation (this can be a credit note for instance, or it can be in the form of a discount on the amount of the fee on the invoice).
They have to communicate the manner of their choice to the end-users in a transparent manner.
When operators wish to compensate the subscribers (or users of prepaid cards) affected in kind (e.g. a free movie), they have to communicate this clearly and give the end-users the choice between this form or a financial compensation.