After more than a year, one child of twins is not registered!

One of my daughters gave birth to twins in the Netherlands in mid-July 2018 (more than a year ago). They registered the births at the SA Embassy before the end of July 2018. After no birth certificates arrived they started follow up. Eventually a year later they received a birth certificate for ONE. In August this year the Embassy recommended that they make a follow-up application for the unregistered twin, which they did. In desperation, my daughter started calling Home Affairs directly from the Netherlands. I decided to lend my assistance as I live here. I have called every week for a month now. I get the same "story" every time - "the matter is marked as urgent" - yet still no birth registration! I have also sent two emails for which I've received no reply or even acknowledgement. Does anyone have a suggestion of how I can escalate this matter?