Pre-paid debt wolves prowling?

New tactic from the pre-paid card guys? (ffrees a uk company). Received an unsolicited card trough the mail. When calling to cancel it I was told I would have to 'activate' the card in order to pass security before being allowed to cancel. It's a security measure you understand. I assume this would cost me at least one monthly charge. Any experience out there? It's a Visa debit so I must be able to go directly to them right?