Worst experience ever!

Worst experience ever! I cannot get a hold of retentions / cancellations department for a week now. Send an email, no reply ( Enquiry Reference Number ***). Tried to call, systems off. Tried to call again just now and call got cut / dropped after holding on for almost 19 minutes. I just need to cancel my contract (I've made my own payments already) - how difficult should it be?? Well, not nearly as easy as collecting a debit order every month!!