Maybe Freank is an Option.
https://fraenk.de/ it is a brand from the German Telekom.
Also sim.de, deutschlandsim.de or winsim.de (a brand from 1&1 Telekom) has a good deal
A other Option is a SIM card from a supermarket like Aldi, Penny, Netto, Kaufland
Thanks. Piwigo looks good. I will try it.
I found a nice comparison on the GitHub