The steps to cancel will depend on how you initially signed up.
If you signed up with Amazon for use on Amazon Fire TV, please follow the steps here:
https://www.amazon.com/gp/help/customer/display.html?nodeId=GDT2SXJJ7K49JKYE
If you signed up with Amazon for use on Amazon Fire TV, please follow the steps here:
https://www.amazon.com/gp/help/customer/display.html?nodeId=GDT2SXJJ7K49JKYE