In Germany in specific building there is only one provider available in your telephone socket, and one in your cable socket in your apartment. Frequently there is no cable socket.
That's not relevant. Over a Deutsche Telekom phone line you can choose an ISP. The ISP sometimes has a layer two connection to you and therefore has their own infrastructure or they have a layer 3 connection in which case you suffer from the Telekom policies.
Layer 2 = their infrastructure connects you to the internet
Layer 3 = theyre literally just a reseller, DTAG is providing your internet connection, the ISP just billing etc.
Layer 2 = their infrastructure connects you to the internet
Layer 3 = theyre literally just a reseller, DTAG is providing your internet connection, the ISP just billing etc.