Only one free trial is available per account.

Payment will be charged to iTunes Account at confirmation of purchase. Subscription automatically renews unless auto-renewal is turned off at least 24-hours before the end of the current period. Account will be charged for renewal within 24-hours prior to the end of the current period at the rate of the subscription.
Subscription may be managed and auto-renewal may be turned off by going to the Settings on the device.
Any unused portion of a free trial period, if offered, will be turned off in Settings on the device.

If you are in a free trial and do not want to continue using our service after the trial period, please cancel your subscription before the end of the trial period. Cancellations that occur after the trial period have ended will incur a charge at the monthly rate of the service you are trialing.