To cancel your subscription click the VPN Administration button on the left hand menu of https://my.liquidvpn.com/clientarea.php 
Click VPN Administration 
Click the service you want to cancel
Click Request Cancellation
Choose to cancel immediately (takes up to 24 hours to process) or at the end of billing period
Either option will stop your subscription before being billed again.

Also Read

Can I use LiquidVPN on a mobile device?
The short answer is yes However we have not released our mobile VPN client yet so you will need...
What support options do you offer?
In order to keep costs down we provide technical support and remote assistance via trouble ticket...
Can I use Bittorrent and P2P?
Yes, LiquidVPN fully supports bittorrent and P2P on all of our servers. We will never censor P2P...
What countries are you have VPN servers located in?
LiquidVPN maintains VPN infrastructure all over the world. We select the best regional hotspots...
Do you offer TCP and UDP OpenVPN connections?
Yes, and we provide several ports for each type of network topology we offer.