I cannot connect Alexa to my Sonos One

I have had my Sonos One device for 6 years and have never been able to connect Alexa to it. I recently tried again and it still will not connect. 
When it prompts me to log into my Amazon account it says my email address is already in use on another account. I have checked the devices under this Amazon account and there is nothing there for me to delete. There are no devices at all linked to my account. 

I have factory reset my device, the app, tried to create a new Amazon account (not possible without a new phone number) and am still unsuccessful. I am very close to giving up again, any suggestions would be appreciated.