Your situation wouldn't be any different if you had subscribed through any other service. They are all non-refundable, as is outlined in the terms shown (and most of us don't bother to read) when subscribing.
You can unsubscribe from your subscription through Roku now. This will prevent the subscription from auto-renewing when your pre-paid subscription period expires but you'll still be able to use it for the balance of your subscription period. Unless your subscription from Verizon has some sort of time limit on it, you could then use it to get your free subscription when the subscription through Roku runs out.
Roku Community Streaming Expert I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well. If this post solves your problem please help others find this answer by clicking "Accept as Solution.".
Streaming Stick 4K+ 3821 | Streaming Stick+ 3810 | TCL Roku TV 43S245/C107X