The European-wide timetable change happens on 10th December. Not all timetables have been published yet. Germany should be added tomorrow or later this week and Interrail/Rail Planner should follow a few days later.
Maybe there was a misunderstanding. Do you have a Global pass or a special Franco-German pass ? The latter only gives you unlimited travel in Germany + travel from your hometown to the border. You cannot transit through Belgium or Switzerland for example.
But if you have a Global Pass you can travel for sure through Belgium ! Keep in mind the mandatory reservations onboard Eurostar Red/Thalys : 32€ from Paris to Cologne. There's a passholder quota so book well in advance.