Energy firms have been told to compensate customers who wrongly had prepayment meters installed in their homes.
There is currently a six-week ban on forcibly installing prepayment meters until March 31.
It comes after British Gas came under fire following an investigation from The Times that claimed the energy giant used debt collectors to break into the homes of vulnerable customers.
British Gas suspended the future instalments, before Ofgem then asked all suppliers to follow suit earlier this month.
The ban includes prepayment meters being installed under warrant and customers being switched over remotely if they have a smart meter.
Jonathan Brearley, CEO of Ofgem, said the energy regulator has told companies it will review what they are doing and if they are following rules.
It's not clear yet how much compensation people could potentially get.
He said: “I am concerned about the way customers in already distressing situations are being treated when suppliers force them onto prepayment meters.
“That’s why, today, we have set out further details on the two investigations, one into British Gas for potential breaches that have been alleged indicating that something went very badly wrong at British Gas and the other into prepayment meters across all suppliers to assess whether this is an isolated case.”
He continued: “I’m telling suppliers not to wait for the outcome of our reviews and to act now to check that PPMs have been installed appropriately, and if rules have been broken, offer customers a reversal of installations and compensation payments where appropriate.
“There will also be fines issued from Ofgem if the issue is found to be systemic. We are taking this issue extremely seriously and customers should feel reassured that where the rules have been broken, Ofgem will act.”
Up until the ban was imposed, energy companies were able to apply for court warrants to enter homes and install prepayment meters if customers have fallen behind on their bills.
Customers must then top-up their meter in order to keep receiving their energy supply, or risk being cut off.
But these are more expensive than paying for direct debit - leaving families more at risk of falling further behind on their bills.
A recent report from Citizens Advice found an estimated 3.2 million people could not afford to top-up their energy meter last year.
It said more than one in five prepayment meter customers cut off in the past year spent at least 24 hours without gas or electricity, leaving them unable to turn the heating on or cook a hot meal.
