I'm so sorry for those of you who've been having issues with Sephora. It really does sound like their software is running amok.
The best person at Sephora to contact about these issues is probably:
Julie Bornstein
Executive Vice President, Chief Marketing Officer and Chief Digital Officer
From working at big companies, I can tell you that it's likely that the customer service people you guys have been talking to have no idea how to deal with the nonsense from the fraud software, and so are just trying to get you off the phone. They probably aren't aggregating the complaints, because when you work at a big company, very few people actually pay any attention to the CSRs who are on the phone with customers (their job is to take as many calls as possible, not to actually resolve issues), when you work in companies like this the last thing you want to do is go to your boss because there's a problem or issue, and because it's unlikely that there's anything the customer service department can do about the fraud software. From her titles, I'd guess that Ms. Bornstein has responsibility for both Customer Service and the website, and might actually look into this if she gets a rush of letters all complaining about it.
About those letters: Keep them short -- try not to go over 1 page in a "normal" size type. Keep them as impersonal and unemotional as you can -- vent here if you need to, write drafts to get it out of your system, but boil it down to the facts: I'm a good customer, I spent a lot of money in a short period of time, I buy extras of my favorite products to give as gifts and your fraud system has flagged my account so I cannot place on-line orders. Your customer service department is unable or unwilling to resolve the issue, so I'm hoping you can determine what needs to be done so that I can remain a loyal Sephora customer.
You guys would not believe the kind of data about you -- specifically and "generically" -- that is available to companies that are willing to pay for it. In a meeting last week, a company was talking about being able to buy the average credit score for residents at a particular address, and what they can do with data like that. You can keep calling customer service and asking "why" your account was flagged, but the reality is that there is probably not anything specific that caused it that the CSR can identify. Any CSR who says it was this or that is probably just making it up to give you some answer and get you off the phone. Contacting Julie Bornstein is probably your best bet.