I know when this discount ends but when does it end?

I work for an ISP where it seems like absolutely no one reads or even glances at their bill before calling in. If people would just take 30 seconds to go over it I swear our call volume would be cut in half. Also this seems like such a stupid thing to get frustrated about, but eventually you start to wonder where all the common sense went…

Me: Welcome to ISP this is LilacPenny how can I help you?

C: Yes so I just signed up and I got a 12 month promo and my bill says ’12 Month Promo’ $70 so how long do I have this promo for?

Me: ……….12 months ma’am……

C: Oh ok so after 12 months what will the cost be?

Me: (trying my damnedest not to be the sarcastic asshole I turn into at work) Your cost will be what you are paying now, plus $70

C: Oh well you should put that on the bill. Anyway that’s all I needed.

Me: Great glad I could help, -customer slams phone down- -I bang my head lightly on my desk and wallow in the stupidity of customers-

Edit: TL;DR “Please read to me this thing I am holding in my very hands.”