'The money was just disappearing in front of us'published at 10:11 Greenwich Mean Time 10 January
The guests on BBC Breakfast were from England and Wales - but the faulty Horizon software was used throughout the UK.
Fiona Elliot, a sub-postmistress from County Tyrone, tells BBC Radio Foyle's North West Today the whole ordeal is still raw.
In 2005, Elliot and her husband bought their Post Office and shop in the village of Clady, but later had to pay accounting shortfalls of £6,000: "I kept putting the money in from the shop to the Post Office to keep it right but we never had a plus, it was always minus, the money was just disappearing in front of us."
Despite urging the Post Office to carry out an audit, she was suspended for weeks before the Post Office confirmed there would be no further action.
She was offered redundancy at a time when rural Post Offices were closing, and resigned in 2008.
In Scotland, the Scottish prosecution service became aware of potential problems with the Post Office Horizon IT system more than a decade ago. Only two convictions in Scotland have been overturned so far.