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

Does LiquidVPN monitor or log users activity?
We do not maintain any logs on users activity, timestamps, or amount of data transferred. We can...
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 LiquidVPN on more than one device?
Yes, you can use LiquidVPN from as many different devices as you want. The only restriction we...
Do you offer a guarantee?
Yes, we offer a money back guarantee. If for any reason you are not happy with LiquidVPN cancel...
Do you offer TCP and UDP OpenVPN connections?
Yes, and we provide several ports for each type of network topology we offer.