Do you have a common name? If you're John Smith, some other John Smith could be trying to get a high tier status match or status challenge from another airline using your account details. I don't see how this would work with different names.

BTW, I wasn't aware that DL is notified when one tries to do a status match/challenge to another airline using one's DL status.

What's your current DL status level?

Have you noticed any security breaches (email hacks, suspicious credit card transactions, miles or points deducted from any account)? In fact, can you verify with a DL agent that no award tickets were issued from your account and that your email address on it has not been changed?