Another Twitter user said they found out their flight was cancelled by checking the website on the morning of their flight.
The decision has been taken due to a huge backlog of annual leave which has seen large numbers of the airline's staff book holidays towards the end of the year.
The company says it is moving its holiday year from the current system of April to March to a calendar year of January to December from January 2018.
Rynanair said the shift meant it had to allocate annual leave to pilots in September and October.
Ryanair Holdings PLC scrapped 82 flights on Sunday, the start of a six-week program of cancellations it's making as it seeks to reduce a backlog of crew vacation required by Irish regulators before the end of the year.
Mr Jacobs said affected customers would have been sent an email.
The Ryanair move has brought "instability" into the Irish tourism market, said Cormac Meehan, who called on the airline to publish a full list now of all the flights they intend to cancel.
The only alternative flight he was offered was on Monday - when he was originally due to be returning to Leeds. "We were left in limbo", Cummings told BBC Radio 5.
Vehicle has issued a statement advising affected Ryanair customers to consult its website (www.aviationreg.ie) which sets out the compensation rights for people affected by the surprise Ryanair move.
For some passengers though, the cancellations have led to lost holidays and even being stranded without help from Ryanair.
He said the odd thing related to customer care, was to say you are trying to improve the airline's operation through keeping more planes grounded.
What rights do passengers have?
A travel analyst said the rule states that if an airline does not offer a suitable flight as an alternative the passenger must be booked on one of the airline's rivals.
That compensation can be reduced by 50 per cent if the airline manages to reroute the passenger and get them to the original destination within two hours for short flights, three hours for longer European Union flights and four hours for those flights outside the European Union longer than 3,500km. If every passenger claims, the total bill could top £100m, with hotel, meal and transport costs on top.