I don't know what's going on, when I went to check the dates and prices on the site, the only month coming up is June, and the only date coming up is the 21st, and it's in red, so I guess that means it's almost full. If you're not sure, you can always phone contiki and find out what's going on.
Are you sure your trip isn't meant to be the 23rd june to the 2nd of july? because european horizon tours are only 10 days long, and the trip you're talking about is 12 days long. also, 23rd june to 2nd july is def a trip because i am on it! hehe
Depending on where you live, some departures have different dates, because the flight takes a day or more to reach the departure city. For example my departure date is the 26th, but my tour won't start until the 28th, because I live in Canada and it's an 8 hour flight plus the time change.
BTW on the Contiki site the 21st is showing as full, so it's probably not canceled
