New Booking

I have an early morning flight from Frankfurt, so I booked an ICE to Frankfurt airport.

Now, I received the notification that it has been cancelled. So what should I do to book a new connection?

I searched for a new one, and found out that there's the same connection. I don't get it why it has been cancelled.

Should I submit a compensation request? Will I get the full refund?

Because the new connections are cheaper would I get the difference refunded?