Happened to me. Cancelled Sky Broadband, CS reps wouldn't acknowledge it. Got sick of the back-and-forth. Sky don't just make you wait on hold for 30 mins, they play ads at you while you wait. Fuck that. Stopped the direct debit.

Debt collectors got in touch years later asking for £50.

I said, "fine, send me a copy of whatever bill I supposedly didn't pay."

They didn't have it. "We don't have any documentation, just pay us."

Escalated to a complaint and they dropped it.

I'd do the same again, but could totally understand why some people wouldn't. YMMV.