Furlough for zero hours

[Cookay]

My DH has had a zero hours contract for 3 years working 3 and then 2 full days per week during all that time. At lockdown his employer said there weren't any hours for him at the moment as the location he works at has closed. He has contacted his employer many times to ask about furlough and only now have they told him he has not been furloughed because he was 'below the threshold' for furlough. We cannot find anything that says there is a lower threshold for furlough. They are saying the 3 months before lockdown he did not earn enough (presumably because he was off sick then due to a leg injury). However, I understand the employer should have looked at the hours worked in Feb 2019 or an average of hours worked 2019-20. He has asked for clarification but so far they have not replied.