Cable Germany & Telekom sensible??

I also have Kabel BW + Telekom installed.

But then I use SAT for TV and telephone + internet via Kabel BW.

According to Kabel BW, Kabel BW without TV connection is only possible with a new connection.

If it is about the flat rate, definitely both. However, I have heard that the flat rates may only apply if a contract with a minimum term (12-24 months) is subsequently concluded. In this case, I would choose a provider and lay an empty conduit with a pulling tape from the house wall to the property boundary (inquire beforehand where a connection could be realized). This definitely makes retrofitting easier and you only have to dig two smaller holes for retrofitting. The same applies if fiber optics or similar should come in 10 years...