Take the next IC to Berlin. Reservation is only optional.

Or are also the next trains not running?

In fact, take any next connection.

What problem exactly did they say is supposed to be for Interrail? Running trains and advising passengers about their travel options is the railway company's job.

In the past-incomprehensible for todays youth, married to their fones: there were printed timetable books-and these could be used to check what other routes there would be and when next train would go etc. The big advantage of this pass is that you can change plans at very last minute in most cases. Using the planner of bahn.com-as we so often explain here-would also give further other usefull connections. Be glad that it was not the strike yesterday in NL-and tomorrow again-which hinders plans-then there will not be any train at all

Ams_Ber has direct trains (that odes not mean no stops-there will be many!) ev 2 hrs as IC (german cars). You can change in Hannover to next ICE for quicker arrival.

You can also go via ICE-change Duisburg-and indeed these ICE are very often cancelled last moment due to insufficient stock ready. 

Both routes have ALTern trains-at least hourly on all the routes by local/regional trains=change more often.