Being Billed out of contract despite being well within 18 month special offer

[#1]

I signed up for new special offer 18 months contract in April which promised me a fixed monthly subscription before call charges etc. Yet I am being billed full whack! I thought maybe I'd overlooked some small print but I've today double-checked the confirmation letter I was emailed.
I'm not keen on phone-lines :'D so I've emailed customer support, but not heard back yet. Wondering if I should put in a proper complaint...Can anyone help please?

[#2 · Accepted solution]

@HollyBlue65 Thanks a lot for reaching out to us on here. I can see that you've raise a complaint here @ https://www.plus.net/wizard/?p=view_question&id=235041968 and as the Complaints team take priority over us on social media I'll leave you in their capable hands. They should take long to get back to you and sort this all out.