Also I'm a bit surprised that Kiwi accepted to deal with this. On the day of departure the airlines are in charge of the ticket and in case of IRROPS the operating carrier in question (FlyBe) rather than the OTA was to arrange the flights to BCN as part of their duties under EC Reg. 261/04 in case of a cancellation of their flight.

Many OTAs would had referred you to contact/deal with the airline operating the cancelled/delayed flight rather clearing up the mess themselves. It seems well handled by Kiwi IMO.