@brian.duffy
When you signed up to 2FA you were given a recovery code so if you didn't make a note of it then check the email you were also sent as you can use this to turn this off and then set it up with your new number.
If you don't have access to this then you will have to contact Sky and ask then to deactivate this for you. Do note that there is a few days turn around on doing this so do not let the adviser wrongly tell you to go to Yahoo as they will not be able to help.
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