At the very least, if you are showing the instalment price, you have to show the number of instalments, and the fact that it is an instalment rather than a pay-as-you-go subscription.
You could certainly argue that describing the plan as $x paid monthly is outright false, when it should be "12 monthly instalments of $x".
You could certainly argue that describing the plan as $x paid monthly is outright false, when it should be "12 monthly instalments of $x".