To mark my Mum's 60th birthday I have booked a cash and miles redemption on SQ PER-SIN-Man

I booked this a few months ago

This morning she tried to choose her seat with SQ only to find that the "airline had cancelled her flight"

On checking checkmytrip I get the following message:

Please note that the Airline has cancelled one or more of your selected flights. No ticket can be issued for this reservation. Please modify your reservation, or contact your travel agent for further information. (9115)

BMI have changed the PER-SIN leg from a 1600 departure to a 1 AM departure and cancelled the SIN-MAN leg completely

Their initial offer was SIN-LHR-MAN in Y

Checking ANA there is no redemption availability in C for any of the legs. However, the original flights are all available in C class for revenue passengers.

I feel disappointed by this as there was no communication from BMI on this whatsover and this is not a good way to mark my Mum's 60th

Any advice would be appreciated.