Former Blue Peter presenter Zoe Salmon and a Belfast-based choral society are among those left frustrated as the fallout from the airline's mismanagement of pilot leave intensifies.
Ryanair had earlier this month said it would cancel 2,100 flights through October because it "messed up" the allocation of pilots' annual leave as it shifts to a new scheduling system.
They include all flights between London Stansted and Edinburgh and Glasgow, as well as those between Glasgow and Las Palmas, Gran Canaria; Edinburgh and Szczecin, Poland; and Edinburgh and Hamburg, Germany.
It said Ryanair had not corrected O'Leary's statement that it was not obliged to re-route passengers on other airlines, and was not telling customers it was obliged to refund expenses they might incur, such as meals, hotels and transfer costs to facilitate re-routed flights.
The grounding of planes to the end of next month was already set to cost the company 25 million euros ($30 million) - five million euros of lost profit and 20 million euros in compensation under European Union rules - O'Leary had said.
The company today announced it will fly fewer aircraft during the winter in a move expected to hit up to 400,000 passengers with cancellations.
Ryanair says the voucher will be sent to all affected customers, who originally paid the full ticket price for a cancelled flight, by Friday.
A 60th anniversary trip to London by St Agnes' Choral Society is now in jeopardy after the surprise announcement. "Ryanair offered to pay back the ticket costs, but it's about more than that". They have also received a 40 euro travel voucher. We had considered rebooking with another airline but the fares are now much more expensive because of the increase in demand, and so we can't afford to go.