I have had the same problem as Dave & Ailsa.
Having changed cancelled outward flights to Mallorca with easyJet I, too, found myself booked to come back three weeks before I was due to fly out, if you see what I mean, and unable to change Friday 23rd's return flight because it was 'not cancelled'.
Having received confirmation of this new back-to-front booking, I felt I had no alternative but to use the usual process to change the return flight, and was charged the online 'change flight fee' - which, since I was handling the booking for three people, amounted to £111.71.
Having spent so long at the computer trying to make sense of the system, I could not face fruitless hours trying to get through on the telephone and emailed easyJet's customer service at 9:00 on Sunday 18th April. My message was acknowledged and a reply promised within 'the next days'. Nothing has been received yet, of course, at 17:30 on Monday 19th.
I shall watch this thread with interest and keep you posted.