Sorry to hear that Welshtraveller,
Its strange for Aer Lingus not to be proactive in this regard. At any rate, please try the Gold Circle department and explain your situation, ie. that you have been waiting for more than 28 days for a refund at this point. Quote your original reference number on the phone and the segment(s) that you could not take because of a closure of the airspace.
To call from the UK: 0871 718 5555
Let us know how you get on,
Regards,
EI Premier