Cerise, Northern Loire-Atlantique hotels

"Asked within allowed timeframe to change from 2 nights to 1 night, which was approved by manager, in a written email response. We only slept there 1 night and checked out in the morning. However, upon check in, we were charged for 2 nights, despite said approval. There was no reasoning with the manager, she insisted that we had no right for a refund because I had said we would leave in the evening, even though we left in the morning, and despite teh fact she had previously approved the booking...