Use the email form here > Apple - Support - Mac App Store - Contact Support
And you haven't done so, change the Apple ID password associated wtih the account > Apple - Support - Apple ID
wife's ccard details to make a 849€ purchase in an other country
Odd that could happen considering credit or debit card credentials must be associated with the same country where you reside.
Billing policy is the same for both the Mac App and iTunes stores.