A crew roster is usually made well in advance of the flight date. An issue for short crewing could be the fact that some members not necessary all were out of hours (law by regulators not airlines). There may have been an issue where standby crew had either allready been used or due to disruption are either out of place or on rest days.
It looks like it is one of those situations however there is no excuse for the lack of customer service as you describe it.
CAA Denied Boarding, Cancellation and Delay: Passenger Rights
Assistant must be provided regardless pf whether the delay is outside the airline's control as follows.
Distance up to 1500km (Delay more than 2 hours) meals and refreshments in relation to waiting time. Two free telephone calls, emails, telexes or faxes.
Distance 1500-3500km (Delay more than 3 hours) meals and refreshments in relation to waiting time. Two free telephone calls, emails, telexes or faxes.
Distance over 3500km (Delay more than 4 hours) meals and refreshments in relation to waiting time. Two free telephone calls, emails, telexes or faxes.
All Flights (Delay more than 5 hours) meals and refreshments in relation to waiting time. Two free telephone calls, emails, telexes or faxes, plus reimbursement of ticket (if passenger decides not to travel)
All Flights (Overnight and more than 5 hours) Two free telephone calls, emails, telexes or faxes, plus reimbursement of ticket (if passenger decides not to travel) plus hotel accomodation and transfers.