I'm sorry that you have had such a difficult experience calling in to get your marketing preferences changed.
As you've asked, I will tell you--yes, I do, on occasion, have to call in to speak to Customer Services or Technical Support, being a long-term customer over 13 years now (going back to the old Ntl days), and I have to listen to the hold music in the call queue as well. I'm no different from anyone else--I don't like to wait in queues--so I understand how frustrating this can be, however, I've always been able to persevere through the hold music and speak to the department required to get my issue sorted out.
You are right--there is no option to choose to change marketing preferences. In this case, you would speak to Customer Services about your account, which would be option 1 (Billing). If you had used the thinking of leaving option, our Retentions team would be happy to get your marketing preferences changed for you or get you through to one of our Customer Service team members.
Again, I have to advise you that we do offer multiple other options to get in touch with us other than calling in such as this Forum, Facebook, Twitter, WebChat and via the post. If you would like for me to look into this for you, I'll be happy to help. Let me know and I'll send you a pm requesting further details.