Plan price is more than it should be after Discount promo ends

I have been on a 6 month discovery pricing for 6 months. This morning I received an email informing that the discovery discount is coming to an end next month. The plan price has been $12.50 + taxes every month, but come March, the plan price will be $27.40 + taxes. Simple math tells that 12.50 x 2 (or -50% discount) = 25.00 and not 27.40.
The user agreement has the plan price of $25.00 set in stone.
I think that the price listed in the email is an error.

Please share your experience.

Edit: how do I tag the moderators so that the ticket is open?