EasyJet complaint: serious illness

My mother has knee surgery coming up which means she is unable to fly at the dates we have booked.
I have requested a voucher but informed this is not an option and i need to change the dates to the flights.

I have spent hours and days after days trying to do this to be told to wait until August as new flights will become available then.
(i have up to one day before the flight to do this so no hurry)

Now deciding to go ahead with the flight changes as no new dates have become available and we are in August, i have been told the fees will go up for charges the following day so i only have today to do so.

They are charging me over £600 to make an admin change which i believe as serious unreasonable.

my mothers consultant does not think she will be able to fly for a year now due to additional surgery needed.
I am at a loss and feel very taken advantage of by easy jet staff.

Please may someone more understanding of this situation get in contact to resolve this situation asap.
I am very unhappy about the help or options to help with this difficulty.

regards
Nicola Potter (K1HKRS7)