VFR C210 with ZTL requested IFR descent through cloud layer; canceled IFR after VMC; but later confused flight status; IFR vs. VFR during continued descent.

Narrative

While on a VFR flight under VFR conditions at 11;500 FT MSL; squawking 1200 and approximately 20 NM from MIKEE Intersection; I contacted ZTL on 120.55 and requested an IFR clearance to descend through the cloud layer beneath me. I was given an IFR clearance and a specific squawk code and began my descent. While in my descent; the Controller further gave me the option to stay IFR with him and he would take me into PDK/Atlanta. If I remained with him; I would have to stop my descent at 5;000 FT MSL; if not; I would have to descend to 3;500 FT MSL to resume my VFR flight. I asked the Controller what was easiest for him; and he responded that there was no difference to him; just that I had to let him know what I wanted to do. I responded that I would just go in VFR. The Controller took that to mean that I wanted to cancel my IFR clearance. I did not understand that my IFR clearance was being canceled and my answer was taken in the affirmative by ATC. I did not understand my IFR clearance was being canceled mainly because I was never told to change my squawk back to 1200; VFR. After being handed over to ATL Approach; I was asked to do something by the Controller and I informed the Controller that I was descending IMC. That Controller informed me that I was not on an IFR clearance and to do him a favor and contact him once I landed via telephone. I complied with his request.