The £50 referral credit will be added to your friend's account and to your account when your switch is complete. Which takes 3 weeks after you've signed up with us. So if it's been less than 3 weeks, it's normal that you don't see the referral credit just yet in your account.
If your switch is complete and after a couple of days you still don't see the referral credit in your account, get in touch with us. We'll sort this out for you. We'll ask you for the details of the referral link you used when signing up.