Most providers construed the law in a way that only new contracts were affected by Routerfreiheit, not existing customers. The Landericht Essen decided that this was not the case. Existing customers can chose their router freely as well.
Get the full decree Im Namen des Volkes (German).
As of today your provider forcing a router upon you is a thing of the past. At least the legal situation says so. But is it really? Several provider establish a free hotspot mesh for their clients now. But only, you’ve guessed it, if said client participates with using the right router.
So what is it?
Here in Germany, your internet-provider supplies the router you will have to use to connect to their service. You want to pick the router of your choice? Sorry, but no!
This has led to many households being stuck with terrible and unsecure routers they could hardly get away from. Bundled up with Störerhaftung this made wireless internet at office or home a risk to get sued. A friend of mine got an adhortatory letter with a 1500€ fine attached because someone hacked into his WPA2 protected wlan and illegally downloaded music. True story.
Routerzwang is scheduled to be burried for good in August 2016. Legislation stepped in to make sure of that and our local internet providers moan and wail.