Are your broadband services restricted due to non payment of a bill? That would explain why it won't let you speak to an agent. If that's the case you can't cancel a restricted subscription.
Here is the normal cancellation procedure: If you are cancelling broadband totally or are moving to Virgin you'll have to contact Sky and give the required notice of 14 days. This link may help https://www.sky.com/help/articles/cancel-sky-broadband If you are changing to another ISP who also uses the Openreach infrastructure then join up with them and they should contact Sky on your behalf. You’ll need to return any loaned router so ensure you get proof of posting and keep it indefinitely.
▪️I AM NOT A SKY EMPLOYEE ▪️ Sky customer since 2001 with: Sky Q | Sky Superfast Broadband | Sky Talk | Sky Mobile NOTE: I only provide help on the forums and NOT via PM