Particularly with large chains, reservation agents are often at a call center far from the hotel. Increase the likelihood that your specific requests will be filled by calling your hotel directly a few days before arrival.
Notify the front desk at your hotel immediately if you are having an issue with your room or stay. Be polite and understanding, but persistent. Your chances of having the problem resolved on the spot are fairly high. Getting compensation after the fact is the exception, not the rule, particularly if you skip this important step.
A double bed in most European hotels refers to two (American) twin sized beds pushed together. A single bed is a twin.
Too late to cancel your hotel room without penalty? Many hotels will be flexible on their cancellation penalty if you call in advance to reschedule for a later date, rather than cancelling outright.