We have only one Sunderberg in Germany, not Sunderburg.
Sunderberg is a part of the community Weste, zip code 29599, about 15 miles northeast of Uelzen.
We have about 6 Oldendorf, the next of Sunderberg is:
Oldendorf as a part of the community Natendorf, zip code 29587
It is located north of Uelzen, 10 miles east from Sunderberg
I hope it help,
Werner