Don't your credit card company usually phone you up ? When I bought my last Dell, I got a call from Barclays asking if I had just ordered from dell, they explained that because I'd renewed my warranty a few months earlier it flagged up as suspect having had two larger than average transactions.
I'd suggest they get into the 21st Century and get Secure Code by Mastercard or Verified by Visa, this was introduced to ensure you have the cards non-electronic info AND the confirmed password.