"Chronoscrolls are purchased and added to your inventory. When used, they EXTEND your subscription by 30 days. They can’t be traded amongst players or sold to vendors, but you can sell them through the trade broker."

The FAQ is also false.

"I already have a subscription. If I use the chronoscroll, will it extend my play expiration date or reset it?

It will immediately add 30 days to your expiration date. It will not reset it."

My original sub expires July 7th. I won't be in town for the next few days to play or to activate the scroll on the date of expiration. So I decided to activate it now, since it suppose to add 30 days onto my account from the expiration date.

Now it say my account will expire July 31st, instead of August 6th. In otherwords, the scroll only added 24 days onto my account.

Why wouldn't you contact support? It's obviously not working as intended, and only extends to the end of the current month, instead of crediting a full month.
You should definitely post about it on the forums where no one can help you.