The charity Citizens Advice said the total bill for the broad collapse of energy firms in the wake of soaring oil and gas prices stands at about £4.6bn nationally.
Some customers were also found to have missed out on credit refunds, as well as struggling to fix inaccurate bills in the process of switching to a new provider.
While smaller energy firms that collapsed typically entered into administration and had their customers moved to a new provider, Bulb’s sizable customer base meant it was too big for the government to allow it to go through the normal process that suppliers entered.
The taxpayer bailout was the biggest since Royal Bank of Scotland, Lloyds Banking Group and Halifax Bank of Scotland in the 2008 financial crisis.
The charity called on the government to “urgently review” how different outcomes of the sale of Bulb may affect customers, to prevent bills from spiralling out of control.
Last month, UK energy regulator Ofgem announced plans...