I had a dating scan done at about 8 weeks from memory. We weren't sure if my last period was just breakthrough bleeding or the real thing so the Dr wanted to check how far along I was so I didn't miss the right time for the 13 week scan. There was someone from this site (can't actually remember who LOL) who obviously didn't have a dating scan and when they went for their 12 week scan found out they were actually 16 weeks! I guess that's the reasoning behind the dating scan - especially if you don't know the date of conception! I would ring back up as they have obviously misunderstood. Hope this helps.