Exchange and refund conditions depend on the train and sometimes on where you booked them, There should be a reference to the applicable conditions in the confirmation emails.

In most cases-if the price you paid covers ONLY the REServ, than its simply a case of ´no good, money lost´ but then these mostly cost around 3-5€/each. You did not specify which trains you booked In IT-for IC its only the 3 or 4 € for the REServ, but the frecce=hi-speed also include a surcharge for that phenomenal speed.

The issue is that in our case we paid via the railpass 282 euro ( 8 pers) for the seat reservations on the trip Aachen-Rovereto(it). This means  35 euro/pers. When we rescheduled our trip for departure one week later , we booked the reservations via the station Maastricht for only 42 euro IE 5 euro/pers.

If we add up all reservations for the 5 day trip, each of us lossed more than 100 euro !

And I cannot call anybody, the NS Maastricht cannot do anything for the cancellation of our reservations, there is no way to contact anybody in person, etc.

Is this about the journey Aachen - Rovereto mentioned here?

Did you book the first reservation for Aachen - Rovereto via Interrail? That's expensive, as I had already explained in the previous topic. They charge 8€ per person and train, which is 24€ in total for the 3 trains mentioned (instead of 4€ when booked via DB). Not sure how you'd get to 35€ though (maybe including the 10€ EC supplement for Italy?).

These optional seat reservations often cannot be changed, so if you change plans, you need to make new reservations. And it sounds like in Maastricht, they booked via NS, also for 4€ per journey and person plus some booking fee.

Aachen-rovereto was split in 3 sections:

Aachen-frankfurt 6 euro

Frankfurt Munchen 6 euro

Munchen-Rovereto  15 euro

Booking fee     6 euro

Shipping cost 2.25 euro

Total  35.25 euro

munchen - rovereto is 2nd class, as we were unable to book 1ste class ; NS Maastricht booked for us the same trip for 5.25 euro--all in 1ste class.

My fustration is that we are unable to change the trip one month ahead without incurring huge costs and without any possibility to ask / complaint with somebody. No telephone number etc.

Sounds like you booked via Interrail indeed, which is expensive for these reservations.

Customer service can be reached here.

Refunds for reservations done via Interrail are explained here (at the bottom).