Finally got through, using the switchboard number ( calling early in the morning, as the phone is not answered in the afternoon). I had even asked Opel Ireland to send an e-mail on my behalf, but no joy for them either. I had ticked the delivery and read request notification, on the many emails I had sent and none came back as read.
There was undoubtedly a copy issued when the car was new, however I am the third owner and the original COC is long lost, I just feel that the certificate should be available from your local main dealer, or should be part of the vehicles log book.