Amazon music unlimited - can't upgrade to family plan

I'm caught in a circular loop. I'm attempting to upgrade from Unlimited to Family unlimited. Amazon forces me to manage my current subscription through the apple store. There is no option to upgrade there, but there is an option to cancel my present subscription. When I do so, it only cancels the auto-update, and tells me that the service will still be available for the duration of the previously paid period (two more months). It will not allow me to end the subscription entirely...I cannot upgrade unless the trial is over. Spoken to Amazon support not he phone for an hour. They have no solution and send me to Apple.

Help!