Thanks for your help, AnotherElk, and it is much appreciated… 
in contrast to the snarky remark about a backup. Exactly what I need, somebody telling me that it is very irresponsible to activate a preinstalled app and not thinking that it might delete all of my contacts without prior asking. How about taking that high horse to frigging Google, Inc or Fairphone Limited, since those are the companies doing things w/o asking for permission, like listening in all the time or purging your contacts because you dared usind a product without umbilical cord to Silicon Valley for a while, were underway, in a hurry and just in need of a frigging ticket for the train, hence trying to install DB Navigator?!?
I’m sorry for exploding in your face, but that is exactly the kind of behaviour which put us “nerds” in the “don’t talk to them they are spooky, scary and mean” bin for DECADES… and I just can’t stand or tolerate it. So to say, it triggers me quite profoundly, as you can read.