Don't tell them about the wrong cord issue, just send it back for warranty work. Or was that costing you 100 euro for the warranty work?
If so, that's not warranty, that's robbery.
If they are charging you for the work, then just open it yourself, as has been mentioned, and figure the drives interface (The outsides change, the inside don't), and get a new enclosure for a fraction of the cost of the "warranty" work.
Or worst case scenario, as it was probably only the power supply circuitry that fried, you could find another one on ebay, and switch out the circuit board. Or just replace the fried components yourself.