I don't think there is a way to cancel a subscription and get your money back for the remaining time. If that's what you want, I will contact the developer and ask about that.
If you don't want to pay money from now on, then you don't need to do anything. The subscription will not self-renew (it's not like a newspaper or netflix abo, where you get new things as time goes on and you have some payment plan).
If you don't want to play any more and want to actually delete the account, that can be done.
Please reply which action you want to take!