Hello, I have left bulb for another supplier and I’m £75 in credit still. How do I get this back and how long does I take?

It will be refunded automatically once your account is fully closed.

It could take up to 6 weeks for your closing meter readings to be authorised by the third-party meter regulator. After that, it could be another 2 weeks before the refund is made. So potentially at least 2 months after you have switched before everything is settled.