Ok, that’s new. I see here that:
17.2.4. Referrers must be existing Bulb members. Recruits must not have already signed up to Bulb or be an existing member, already on supply with Bulb, or a member of Bulb in the preceding 12 months, under any email address or alias.
That is a recent change and has not been announced by Bulb as far as I can see.
Sounds like you’re just a little too late.
You should have still got the original £50 as part of your total credit refund when the account was closed. Of course, your refund might still have been less than £50 depending on your final bill, but that doesn’t mean you didn’t get to “keep” the referral credit.
17.2.11. Rewards are not transferable and may not be auctioned, traded, bartered or sold. Upon termination of the programme or any portion thereof for any reason, or upon cancellation of a user’s Bulb account for any reason, any unredeemed rewards accumulated by the user are forfeited. Rewards that have been added as credit to the user’s account are considered redeemed, and will be refunded to the user on termination of a user’s Bulb account.
It sounds like you might be confusing your direct debit payment for “the bill”. They are not the same thing. Was it just your direct debit creeping up, or actual monthly increases to the cost of your energy in terms of unit rate (pence per kWh) and standing charge (pence per day)? I suspect you mean simply your direct debit was increasing, not the actual cost of your energy.