Alexa can be hit or miss it seems. Have you tried the askAlexa app from here? There are several topics on it here.
Last night, I told Alexa to turn off backporch light about a dozen times and she kept replying there was no device called that. I cussed at her & she said thank you for the feedback. A few more tries and she turned off the light. Was able to turn it back on and off again without issue.