Two months after leaving the Celebrity Big Brother House, Preston's chosen charity is still waiting for the cash.
The Ordinary Boys singer, from Worthing, picked St Patrick's homeless hostel in Hove to receive the money raised by his telephone votes in the reality TV show.
But the shelter, which is facing an uncertain future because of lack of funds, has not yet been paid the £40,000 it was promised.
Preston had no idea that the charity was still waiting for the money.
The indie musician, whose full name is Sam Preston, used the Big Brother experience as a launch pad for his band and to raise money for St Patrick's.
In the past eight weeks sales of The Ordinary Boys' album have soared and the re-release of their single Boys Will Be Boys made it to number three in the charts.
Their success was buoyed by the media interest in Preston's romance with Big Brother winner Chantelle Houghton.
When Preston, 24, was told St Patrick's had not received any cash, he said: "I didn't know that I didn't know the money hadn't come through.
"I'm going to make some calls. I'll sort it out."
In January, Brighton and Hove City Council decided to stop paying the hostel an annual £200,000 grant deciding the money could be better spent on other homeless facilities.
Caroline Searle, spokeswoman for St Patrick's, said: "The money from Preston being on CBB is vital to the hostel.
"We have to fund our work ourselves now but we're still waiting for the money to come through. We last spoke to CBB six weeks ago and they reckoned we would get about £40,000.
"The hostel runs on a Good Samaritan basis and doesn't turn anyone away."
The non-payment was exposed by celebrity magazine Reveal.
A spokeswoman for CBB told Reveal: "It takes a little time for the money to trickle through. As soon as we receive it, we forward it to the charities but the process does take three months."
The city council has given St Patrick's a one-off payment of £50,000 to modernise its services, including creating private pod-type rooms for residents.
It cancelled the annual grant because the shelter did not query whether its users had connections to Brighton and Hove.
The council said this did not fit its policy of providing homelessness services only for local people to avoid attracting more to the city.
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