Medicare 1500 Form Question - Anon

Can anybody PLEASE tell me the correct way to put a patient's last name on the 1500 form for a Medicare patient when the last name has three parts separted by spaces, i.e. AA BB CCC, FirstName, MI, which is the exact way the name is on the patient's Medicare card. Medicare denied the claim. Then we put the last name as AABBCCC, but it was denied again. I had a similar problem a few months ago when a patient had a suffix after the last name and was able to call Medicare and was given specific instructions on how to fill out the demographic info in the system so that it will populate the 1500 form the way Medicare (and ONLY Medicare) wants it. Since we don't know how Medicare has this patient's last name in their system, we can't get past the automated system to talk to a human for instructions. Any help would be greatly appreciated! If I didn't explain this well enough, please let me know.