Anyway they now say they still want a letter from the NSO confirming our marriage appears in their records. I was just about to hang myself when my wife saved the day

Our first daughter was born before we were married so her birth certificate was marked 'illegitimate'. After we married I said to the wife we better fix that so it does not cause problems later. As part of the process we had to get the very letter the passport office is asking for and my wife found it in our document files at home

Some here will know what this is. It's a Cenomar which is a certificate of no marriage. Used mainly to ensure people are single before entering into marriage it is also used to check and identify a marriage in the NSO records. We have two of them one search on my name and one search on the wife's both showing our marriage is recorded at the NSO.
Phew! Let's hope we can put this to bed now.