@Claudi. A few corrections are needed:
Eurostar reservations are quite strictly non-refundable and non-exchangeable.
Eurostar reservations can be changed for a fee of 15€ via the Eurostar website, using "Manage Booking”.
You can contact our customer service team to request an exceptional refund on your behalf, but based on experience this will likely be declined due to the fact that they did provide an alternative.
EU legislation sees this differently, see Regulation 1371/2007, article 16. When a delay of at least 60 minutes at your final destination is expected, you have 3 options, one of which is a full refund.
I am unsure which trains you booked to get from Paris to Milan, but most French trains are at least 60% refundable provided that a reservation is canceled at least two days prior to departure. You can cancel a reservation by clicking on the trash bin next to the relevant reservation in your overview. Reservations on Italian trains are non-refundable but they are exchangeable. You can request a change of departure either locally at the station, or by contacting Trenitalia's customer service. More info here.
It's usually not a good idea to cancel yourself when the timetable changes after you booked, because then you give up your rights under the EU regulation (see above).
Therefore, please unmark your comment as the "best answer”.