Hellenic Seaways has suspended operation of the Flyingcat 3 and Flyingcat 4 from the Western Cyclades route for the whole summer season of 2016.
Basically this means that the islands of Sifnos, Serifos, Kimolos, Milos, Folegandros and Santorini will no longer be serviced by the Flyingcats.
Of course all clients that have already booked tickets will be reimbursed their ticket value.
There are however alternatives for most of the above connections with other shipping companies.
If you have tickets for any of the above islands with one of the two above mentioned ferries you should contact the agency that you made your bookings with and ask for alternatives.