For some more advanced support they may charge.
They certainly shouldn't for clearing all your DRM device registrations.
The Adobe registration system seems quite error prone, as well as the irritation of no website to check and update them.
It may well be that it has miscounted, maybe if you registered a device more than once.
I have heard that some representatives don't know how to reset the registrations; in that case hang up and try another representative and hope they are better trained.
If your problem is with another device using Overdrive, Bluefire, Aldiko or similar third party app, it is recommended not to mention that app when on the chat, just mention that you have run out of authorizations (E_ACT_TOO_MANY_ACTIVATIONS) . Thanks to AJP_Bear for that tip.