installation - QGIS update from 2.14 to 2.16 failed on Ubuntu 14.04

Until yesterday my whole qgis and python-qgis worked fine with version 2.14 under Ubuntu 14.04. After a simple sudo apt-get update and sudo apt-get upgrade qgis failed to update... Several attempts to reinstall it with different versions failed.

Current error message (for version 2.14.3) goes like this:

qgis-providers (2.14.3+dfsg-2~trusty1) is configured ...
/usr/lib/qgis/crssync: symbol lookup error: /usr/lib/libgdal.so.20: undefined symbol: GEOSDelaunayTriangulation_r

I also tried to reinstall all gdal libraries - not sure if I got all?!

Maybe it is somehow related to this one: QGIS 2.14 fails to install on Ubuntu 14.04 ?

UPDATE:

Trying to install version 2.16.0 it gives different but similar error:

/usr/lib/qgis/crssync: symbol lookup error: /usr/lib/libqgis_core.so.2.16.0: undefined symbol: GEOSNearestPoints_r

UPDATE Sources:

For version 2.16.0 there are these sources in /etc/apt/sources.list:

deb http://qgis.org/debian trusty main
deb-src http://qgis.org/debian trusty main
deb http://qgis.org/debian trusty main
deb-src http://qgis.org/debian trusty main

which are all the same, right?

When I do apt-cache policy qgis it gives me:

qgis:
  Installiert:           1:2.16.0+20trusty
  Installationskandidat: 1:2.16.0+20trusty
  Versionstabelle:
 *** 1:2.16.0+20trusty 0
        500 http://qgis.org/debian/ trusty/main amd64 Packages
        100 /var/lib/dpkg/status
     2.0.1-2build2 0

        500 http://de.archive.ubuntu.com/ubuntu/ trusty/universe amd64 Packages