So basically you have redeemed the Bond but now want to cancel the redemption. The only other purpose for a Bond is to sell it if you don't want to redeem it.
I am going to say this is a very unusual request. Jagex will cancel redemptions if a player has redeemed a feature from the Bond that they cannot use i.e. early name change. In a case like that the Bond redemption is cancelled so that the player can redeem it for membership (which can be used).
However you have redeemed for membership and now have changed your mind about getting membership. This is not a refund situation, this is about cancelling the Bond redemption. To contact Billing Support to request this, use the 'Contact Us' button at the bottom of this page. While the page itself is not exactly on the right topic, it is the most appropriate contact point to request a cancellation of a redemption.