Odd, if you received the email notification the payment should show up. When you log in to your dashboard at https://account.bulb.co.uk and select ‘Refer a friend’ (or, in app, ‘Referrals’ -> ‘See the status of your referrals’) does your friend show up as completed (or pending)?
If it’s completed, you should have £50+ ‘total rewards’ credit and your Bulb account should have an additional £50 in it. If it’s still pending, with the date still on the 28th, drop Bulb a line at firstname.lastname@example.org - if it’s still pending, but has a future date, then there may have been a problem in your friend transferring across which has just delayed things by a few days.
If it’s not showing up, and you know your friend hasn’t cancelled the switch (which seems to be the common reason for referrals not completing), just drop Bulb an email and I’m sure they’ll check things out for you.