A few days ago - I had some strict requirements of extremely low monthly cost (I only need it for sending and receiving SMS and for signing up for certain german services that require a German number) - so I want with O2 Prepaid. There are a lot of instant sign up eSIMs that are data only, which is not what I'm looking for.

I would be surprised if you're talking about an eSIM service that give you a phone number.