At what point can I either request a decrease of my monthly payment and/or a refund of the credit?

Hiya, can anyone tell me what their monthly direct debit amounts are in comparison to their actual usage amounts?
For both my electricity and gas I am paying a monthly debit of around £100 and have been doing so since I joined. My usage…(considering we are hitting the winter months) has only just peaked at about £75…which I’m sure I shall decrease because I shall be turning everything back down now haha
So I’m sitting on what is a considerable amount of credit in my eyes… at what point can I either request a decrease of my monthly payment and/or a refund of the credit? I’d expected to pay more than my usage through the summer months and it even out for the winter but it seems I’m still overpaying. Anyone else had/got this experience?

Ideally if you keep 1-2 month credit then anything above that can be transferred back to you.
I would contact Bulb to discuss.