The Coalfields Regeneration Trust was one of a number of charities which put cash into Mexborough Resource Centre, on Dolcliffe Road, which saw around Â£900,000 in grant money spent on it around 10 years ago.
Now bosses say they are disappointed with the sale, without consultation, and are calling for talks to explain the move.
CRT chief executive, Gary Ellis, said: 'The support that we have given Mexborough Community Partnership has been well documented over the years. As with all funding applications and contributions, in each instance we followed the necessary and robust governance that we have in place.
'It is therefore disappointing that the building has been sold for less than market value and without consultation, particularly as the funds we have allocated have ensured the facility continues to deliver services that meet with the complex needs of local residents.
'We will be pursuing the group and those involved for further clarification to ascertain how this decision was reached and what it means for the future. As ever, our focus remains on supporting the coalfields and the communities that we serve.'
Meanwhile, Doncaster Coun Bev Chapman has asked the partnership if she can join the board of the organisation. She said: 'As Mexborough Councillors, we have often wondered what exactly does Mexborough Community PartnershipÂ actually do and what value to they bring to the town? If local Councillors were more involved in MCP...then we could alleviate some of the growing concerns and reassure local residents that this is a good deal for Mexborough.'
In a letter to MCP members, Partnership chairman Sue Phillips explained that the partnership lost 40 per cent of its business in 2017 when one of its main tenants gave notice and left, and then Dearne Valley College announced it was leaving the site due to funding cuts. Within three months, the loss of business had risen to 80 per cent.
She added: 'Such a loss of revenue meant that we were no longer financially viable. If we didn't act quickly, the business, including the charity, would have had to enter a process of receivership, which sadly would have beenÂ an inevitablity had we not got into talks with Mexborough Business Centre.
'The sale of the building has been carried out with the involvement of our solicitor and the charities commission. The charities commission had no objection to the sale of the building in order to sustain the charity for many years to come.'
The building was valued at Â£200,000 to Â£250,000 on an open market, but the sale process could have been lengthy, she added, and their lawyer felt that the figure may be unrealistic and not achieveable in its location. Several buildings had already stood empty for several years.
A local auction house quoted Â£100,000, withÂ maximum of Â£120,000 at auction, and a cash offer of Â£80,000 was received and rejected.
She said under the terms of the sale to Mexborough Business Centre, the partnership will receive Â£120,000 over 10 years, including a Â£20,000 deposit. MCP wouldÂ also get 10 per cent of any increase in its value that may arise from any future planning applications if its sold again under different planning conditions. If there is a default in the deal, ownership reverts to the MCP, which also gets free accommodation under the agreement.
Ms Phillips added proceeds of the sale would go towards employingÂ training schemes for local people, help for community groups, environmental projects, schemes to help address loneliness and mental health issues.
She said: 'The directors believe this to be the best deal they could possibly get, given the circumstances. Mexborough Resource Centre will remain part of the community, Mexborough Community Partnership will have a regular income, that will be used to benefit the people of Mexborough.'