Complaint Review: First National Collection Bureau

I AM WRITING BECAUSE FOR THE PAST COUPLE WEEKS THIS COLLECTION HAS BEEN CALLING ME AND LEAVING ME MESSAGES REGARDING AN IMPORTANT BUSINESS MATTER, BUT I HAVEN'T RECEIVED ANYTHING IN THE MAIL FROM THEIR OFFICE REGARDING AN COLLECTIONS. SOMEONE IN AN EARLIER POST SAID THAT TO SEND A CERTIFIED RETURN RECEIPT REQUESTED LETTER TO THEM ASKING ABOUT THE DEBT IF THEY HAVE SENT ME A LETTER BUT DO NOT ANSWER THEIR PHONE CALLS. MY QUESTION IS IF I HAVEN'T RECEIVED A COLLECTION NOTICE FROM THEM SHOULD I STILL SEND THE CERTIFIED RETURN RECEIPT REQUESTED LETTER , OR WHAT SHOULD I DO?

THANK YOU

Nicole
ANAHEIM, California
U.S.A.