Perfect, what a big relief!
I guess it has to do with my dualsim.
My second simslot is always named like the first simslot.

I did not notice first, because i was using two sims of the same provider (2x Debieltel/Eplus).
Now i testet a vodafone sim but it is called mobilcom-debitel like the others instead of vodafone.
I can not connect to vodafone net manually.
When i select "search for networks" in mobil settings, i see vodafone net, but when selected it changes its name to mobilcom-debitel.
Even if vodafone is the only sim and in slot1.

Is there a way to reregister the simcards or delete the previous entry?

EDIT:
Mystery solved!
Still no clue about my simcard naming, BUT i was not aware that my installed rockpoold version has the nasty "phone freeze on call notify" bug.
I got aware by reading the rockpool thread and screamed horray

Keep calm, nothing happend, problem is solved.