The eManager software only works on a newer system, the Strata CIX. The Strata DK 40i system is programmed only by a display handset. When you said that your phone type was a DKT3020-SD, then it was assumed that you had a Toshiba CTX/CIX system . Usually the older systems have DKT2000 series phones, but the DKT3000 series phones will work also.

I have seen similar situations when removing extensions, and the ringing extensions get removed from the system. The other issue is if you have a voicemail system. I would call to your system and press 0 to make sure that you can retrieve the messages .