A computer glitch more than 12 months ago led to a pensioner being overcharged by as much as $900 on her electricity bill.
The woman rents her Corrimal unit through Huxley and Partners real estate, run by Charles Hegyi, who volunteered to deal with the issue on her behalf.
In a Mercury story two weeks ago, Mr Hegyi said the woman received two bills from Origin Energy in the last 12 months in excess of $500 each - both were at least $400 more than previous bills.
Each bill was calculated on an estimated rather than an actual meter reading.
Estimated readings most commonly occur when there is something restricting access to the meter box.
When Mr Hegyi began calling Origin and Endeavour Energy - which was contracted to read the meter - he was told several times there must have been something in the way that stopped the meter from being read.
But there is nothing obstructing this meter box - anyone passing by on the footpath could easily read it.
Mr Hegyi began investigating the matter six weeks ago.
Aside from a "goodwill gesture" of a $150 cheque from Origin, Mr Hegyi said "nothing's happened".
He said spokespeople from Endeavour Energy just this week admitted the delay was at their end. But he cannot believe it took them six weeks to admit this.
"Everyone I've spoken to [at Origin] since this all started have all told me that they've emailed Endeavour, they've rung Endeavour.
"Then I was astonished [on Monday] when I rang to find that nothing had been done.
"All those attempts from Origin, and some from myself, had fallen on deaf ears."
And now the pensioner is still $750 out of pocket - taking into account Origin's $150 cheque - because she paid those massive electricity bills calculated on estimated readings.
Mr Hegyi was critical Origin wouldn't refund more than $150, reasoning that if they were prepared to estimate how much she owed them, they should be prepared to estimate the refund.
Yesterday, two weeks after the Mercury became involved, six weeks after Mr Hegyi began his efforts and more than a year after the first error in her bill, Endeavour Energy has admitted - and rectified - its mistake.
An Endeavour Energy spokesman said the issue arose after the company changed the meter at her home in February last year.
"At that time, we did not update [her] records in our system with the new meter," the spokesman said.
"This has now been corrected and the meter data will be provided to Origin by the end of this week to allow them to understand [her] actual consumption since April 2012."
He said the new meter was being read but not linked to her account in the system, prompting the estimated readings.
This data is now been provided to Origin to allow them to calculate the woman's actual consumption since April last year.
"We deeply regret any anxiety or hardship caused over this period," he said.
"This was due to a fault on our part and not Origin.
"We would also like to thank Mr Hegyi for bringing this matter to our attention so it could be investigated and remedied."