New customer getting billed for free broadband?

[#1]

Hello, I've just signed my Mum up to PlusNet for broadband & phone, they've messed up the first D Debit bill but that's supposed to be sorted now after a phone call to customer services who were very helpful after waiting for ever on the phone to speak to someone.
My query is when I signed my Mum up it was advertised as free broadband but now Plus net say she has to pay £2.50/ month why is this??? So free doesn't mean free? I'm confused now as I thought I read & re read everything before I signed my Mum up.

[#2]

Did you sign up prior to the 8th July as I believe that's when the free offer began, before that the offer was for £2.50 per month.

[#3]

Thank you for your reply Chris, yes I signed her up on May 27th 2015, the TV Ads ect are really really misleading if this is the case, I read & re-read before signing her up and I still got caught out, I feel we've been done!!! it's not all about the money but the fact we/ feel we've been misled, we are very disappointed too. Regards AIM.