Do Dorf letting agents actually reply sometimes ? (Duesseldorf)

My boyfriend and myself have started looking at flats in Duesseldorf and have contacted several agents via websites such as Immonet, Immoscout, Immobilio, Kayaldo.... but hardly get contacted back by the agencies. My boyfriend is a native from the town but doesn't live there anymore - however obviously speaks perfectly german and we have a jobs which allow us to aim at a 2 bedroom flat in the centre (ok, with a balcony and a car park but I don't think it is the reason why we get no reply to requests).

I'd like to understand why, any ideas ?