General aviation pilot reported there was no information stating that there was a Tower or frequency other than CTAF at COE and the reporter nearly landed without contacting Tower.

Narrative

While on a long; cross-country flight; I decided to stop at COE for fuel.I consulted a current paper sectional chart; the current updated database in my flight planning software (Garmin Pilot); the NOTAM" menu for COE in Garmin Pilot; the current; updated frequency database in my radio; and listened to the COE ATIS from 25 miles out.NONE of these indicated the presence of a Control Tower at COE; nor any frequency other than CTAF - 122.8. All agreed that the CTAF was 122.8.I announced my position and intentions to land on Runway 20 multiple times on CTAF; starting 15 NM out.When I was downwind abeam and about to lower the landing gear; a voice identifying themselves as COE Tower came over CTAF saying that I needed to talk to the Tower and to immediately make a right 360 turn - towards mountainous terrain; at low altitude and slow speed. The voice gave a Tower frequency; which was garbled; and resulted in further confusion and delay in re-establishing communication. I had to call back on CTAF to get them to clarify the Tower frequency. Once communication was re-established on the new Tower frequency; I was cleared to land on 20 as I had been set up.This was dangerous; setting up a situation where not all aircraft in the area were in communication; when they would have good reason to expect that they were. It caused confusion and unnecessary complication and distraction during the landing phase; and was completely avoidable had the COE Tower frequency been properly charted and updated in the databases; or mentioned on the ATIS; or if COE Tower; who were obviously on CTAF; responded to any of my early announcements over CTAF."