Just a shot in the dark, in case someone knows this:
Are the toilet outsources to Sanifair and co. at DB train station under DB responsibilities or one should contact the contracted company ?

I was a bit miffed to have to pay one euro for a dirty toilet, get 50 cents back as a voucher which is not accepted in any shop of the station. The nearest partner was 60 km away. I find it disingenuous that they implement this system without a partner at the station that accept vouchers. DB washed their hand of the complaint saying that the toilet owner is responsible. I have difficulty with this concept as the station is owned by DB.

On à related but separate note, is this correct shops and restaurants must provide free toilets to their customers by law ?