ultimately its negligence on your referee’s part, not on ucl’s part. they made the decision fairly based on the information they were given, as unfair as it may be in retrospect. it would be understandable if your referee contacted them before the 15th jan and ucl were negligent in changing them, but any time past that doesn’t fulfil ucl protocol, as harsh as it is.
ultimately predicted grades are only one of the factors for getting in, but if you really want to go to ucl you could reapply thru ucas extra OR reapply next year with your actual results.