@merton69
I'd been meaning to cancel, ever since my sub reached ~£40/month (average channels package, no special-request channels) but I had a backlog of dozens of hours of unwatched progs and Sky warned me I'd lose access to these. Last year, my subscription was inexplicably increased by 50% and that was the last straw.
*Write* to their HQ, quoting your subscriber number, requesting cancellation and specifying an end date*. Don't bother with any backstory, beyond "I can no longer afford your product", maybe thank them for 10+ years of, otherwise satisfactory, service (to stress that you were a loyal customer).
If you phone them, expect to rack up an hour or more on your phone bill (unless you can persuade them to do a ringback).
* actual end date depends on your direct-debit day plus 1 month, since you pay in advance.
Within days of my end date, they were sending me offers of 12 months at 25% of my previous rate.
I was incensed to think that the increase they'd slapped me with was just subsidising the discount-rate offers for new (or canny) customers.