Why do I have £109 taken on my bank account when my consommation is £71?!

It’s just the way Bulb operates. The regular direct debit payment taken from your bank account is a fixed amount not related to consumption. Although the amount is fixed you can change it whenever you like to a different fixed amount. Or you can ask Bulb for a refund of credit.

Ok thank you.
However, when my consommation increased, Bulb also increased my monthly payment automatically.

To put it more accurately, the amount taken from your bank does not vary in line with fluctuations in monthly consumption.