How much did you need to pay?-without the 2€ extra handling.

Seat is usually 5-6€ (in IT often just 3 on daytime IC-dk for ICN), a couchette is 20 or little more, often even indeed a little more as hostelbed, though in practice you get far less as that for the money.

Oh wow - we paid about 40$ (each)… Does that sound excessively expensive?

I was more wondering about the layout - does 5C, 5D, 6C and 6D sound lie they would be in the same couchette>

No that price sounds about right for couchettes. Unfortunately, @mcadv does not seem to know the correct prices and didn't check them.

I'm not sure if those couchettes are in the same compartment although if you booked them together they should normally be. Trenitalia seem to have changed the numbering of their couchettes to a non-standard scheme and I can't find any coach plan with numbers online.

I did a reservation on the same train for july and it says carriage 8 / places 51 +

5C / 5D / 6C / 6D is normally the numbering scheme for a seating car in this train. 

So I don't think you did book a couchette at all...  you may verify this with your carriage number...

That may be the case indeed. Seats are in coaches 1, 2 and 3 in this train. The numbers mentioned are around 1 table.

Thanks everyone, yes, there is a clearly an issue with the tickets. I’ll contact them to sort it out.

Thanks for your responses!