Ann Probyn raised the issue with Gordon Brown in March
Foreign Secretary David Miliband has said the treatment of a woman who sought answers about her son's death in Afghanistan had been "inexcusable".
Gordon Brown told Ann Probyn in March that officials would look again into the death of her son Daniel, killed by a roadside bomb in 2007.
Mrs Probyn, who says his vehicle had inadequate protective equipment, said she had heard nothing for seven weeks.
Officials said Defence Secretary Bob Ainsworth had spoken to her on Sunday.
Mrs Probyn told Mr Miliband of her concerns when they both appeared on Sunday's Politics Show on BBC One, which was hosting a debate with the foreign affairs spokesmen of the three main parties at Westminster.
On the same programme in March, she pressed the prime minister over her son's death - which she has blamed on the lack of electronic equipment designed to counter explosive devices - and been told that the matter would be investigated further.
But rather than being contacted in person, she said all she had received since then was a Labour manifesto and a standard letter.
"Your leader promised to look into the events of my son's death," she said. "I was given a card, I phoned this number and, for seven weeks, I haven't heard anything. Why should I vote Labour when they are not doing anything to help me."
In response, Mr Miliband said he understood that MoD officials had contacted Mrs Probyn and that Defence Secretary Bob Ainsworth had called her twice personally but Mrs Probyn said this was not the case.
When the foreign secretary said Mr Ainsworth was "waiting" to speak to her about the issue, she said she should not have to call him and that he should contact her instead.
Mr Miliband replied: "I don't understand why that has happened. It was obviously completely inexcusable if you were promised a phone call and you didn't get one. I don't understand how that has happened."
It is understood that government officials recently contacted the Probyn family but did not speak personally to Ann Probyn and that the issue is being investigated.
The foreign secretary said a coroner's inquest in 2008 into Mr Probyn's death had concluded his death was not caused by inadequate equipment.
But he said it was "absolutely clear" that the government was looking after British troops fighting in Afghanistan.