Martin Lewis has been forced to change his energy advice after major suppliers decided to make a U-turn on their previous comments.
Mr Lewis had told customers they would be charged a cheaper rate if they topped up a non-smart prepayment meter before the 54 percent price cap rise on April 1.
The money expert said he had been told by all major firms, except Scottish Power, that customers would be charged at the rate of the day you top up.
But now, firms have backtracked on their earlier confirmation, leaving Mr Lewis having to retract his advice.
Speaking on his MoneySavingExpert website, Mr Lewis said: “A few weeks ago, we said that if you top up a non-smart prepayment meter before April 1's 54 percent energy price cap rise, you will be charged at the rate on the day you top up, until you top up again.
“We had written confirmation of this from all major firms (except Scottish Power who disagreed) and the regulator, Ofgem.
Martin Lewis
Twitter/MartinSLewis
A 54 percent price cap rise will be implemented on April 1
Andrew Matthews
"The obvious tip therefore – for anyone who isn't in energy debt and could afford it – was to max your top-up before March 31 and not top up again until it was all used.
“That way, you could keep using energy at the lower price as long into April as possible. Again, that this would work was confirmed by the regulator."
He added: “At the time, we reported Scottish Power's rejection of this tip to Ofgem to see if it was breaking any rules. Ofgem has been investigating, and it has now got back to us with some surprising findings.
“Separately, we contacted E.ON after some MSE users reported that it had given them contradictory information to what we'd said. It then gave us a statement seemingly at odds with its original one and started to say that any energy used in April would be charged at April's rate regardless.
“I discussed this with the regulator on March 22, and wrote provisional findings then as I wanted to get the information out as quickly as possible that the tip will not work in as many areas as we had first thought. We gave them a deadline of today for cast iron information.”