Thank you for your help.
I retried it two times with many (several hundred) addresses in my old seed. Didn't find
a iota anymore. When I performed it the first time I gathered all my balances correctly and
transmitted it to the new seed. Where they never arrived ...
I copied and pasted a my new seed incorrectly (I wrote it in a file and copied from there).
This is possible, of course. But I did it carefully.
The transaction is still on the way
A software bug ...
It would be nice to have a kind of "debugging software" which generates my old addresses from my old seed and looks up in the tangle for all transactions, at least the lastest ones. Maybe such a tool exists?