SV is becoming a joke and a very dangerous one at that. EU261 only gives very partial protection here, even if you fly to or from Europe. For the inbound section SV is a non EU carrier and that does not give a lot of rights. And in any case, if they do a schedule change 2 weeks in advance, as they did, EU261 gives you nothing. They apparently play hardball in such cases now. They won't rebook you on another carrier, even if they cannot offer a flight themselves close to the original flight dates. The only realistic option the OP had was to cancel the ticket and getting a refund when things changed in April. They probably want to teach us not to do what OP did - fly in the outbound and hope SV will solve the inbound issue. With SV now changing schedules and dropping destinations all over the place, I would say - if you have an SV ticket, ensure you are flexible with any other add on bookings you have (hotels, positioning flights) and that if you have to drop them since cancelling SV with a refund is the only thing you realistically can do, costs are minimal. And of course, this ' wait till 24 hours befor you fly' is a risk you never can take.

SV seems in many ways an airline in financial bad weather - dropping the free stopover hotel, dropping rebookings on other airline in case of major schedule changes, and doing schedule changes and dropping destinations all over the place, apparently in a bid to optimize revenue.