If your Netflix subscription is included as part of your Sky bill, you have to contact Sky direct in order to cancel Netflix. Head to sky.com/upgradenetflix to find out how.
Netflix is included with Sky's Ultimate TV package, but if you took it out before 4th March 2020 and haven't changed your options, you'll have the Ultimate On Demand package. If you have Netflix though Sky, you'll need to cancel your Ultimate TV (or Ultimate On Demand) package to get out of Netflix. This is a rolling 30-day contract, so it's just like cancelling Netflix normally. But you may have signed up to longer terms (12 or 18 months) to begin with, and may have to pay an early termination charge if you're still within that time period.
If you already had Netflix before you started taking it through Sky, Netflix will keep charging you, so you'll have to cancel direct with them too. But if Netflix doesn't have an up to date payment method for you, your account will go on hold and you'll need to reactivate your account with Netflix if you want to keep your subscription active, or cancel direct to stop subscribing.