Considering you were asking about how to send in the RFE response back on Nov. 25th, and you were told to wait for the mailed version which would include the information you were seeking, when did you receive the mailed RFE and precisely when did you mail back your response.
Assuming you mailed back the response on Nov. 25th, you do realize there were two public holidays, and four weekend days between Nov. 25th and today, Dec. 9th for you to be stressing about not hearing back, considering today is barely past noon as a matter of fact?
Anyway, to directly answer your question: if you were able to track the package and have proof of delivery, then that’s all you need to demonstrate compliance as required, in the unlikely event they misplaced the response.
It is not unusual to not receive any update for quite a while after a RFE response gets sent, in addition it can take much longer during the holiday season, so more patience is required.