Address for Midland Funding LLC/Midland Credit Management, Inc.?

I received a dunning letter from MCM and I have five addresses for them and counting. Where do I send my debt validation letter?

[Their website gives this address:]
Midland Credit Management, Inc.
8875 Aero Drive
Suite 200
San Diego CA 92123

[This website gives this address:]
Midland Credit Management, Inc.
P.O. Box 939019
San Diego, CA 92123-9019

[They say Midland Funding LLC purchased the debt:]
Midland Funding, LLC
227, W Trade St Ste 1610,
Charlotte, NC 28202-1676

[Asking me to send payment to:]
Midland Credit Managemnt, Inc.
P.O. Box 60578
Los Angeles, CA 90060-0578

[Dunning letter sent from:]
MCM
Dept. 12421
P.O. Box 603
Oaks, PA 19456

Thanks in advance for any insight.