MASON, Ohio -- Carlie and Billy Costello know that their 5-year-old daughter, Maddie, would make an excellent big sister. They adopted her in 2011 with the help of Independent Adoption Center in Indiana; they returned to the agency in 2014 to begin the process of finding Maddie a sibling.

"Thank you for taking the time to get to know us," the couple wrote in a letter to potential birth mothers. "We’re excited to get the chance to know you, too."

In the three years between the start of the second adoption process and the abrupt Tuesday closure of Independent Adoption Center, the Costellos poured countless hours and more than $12,000 into their efforts. They passed a homestudy. They provided the center with marriage certificates, tax returns and other legal documents to prove that their home would be a safe, stable place for another child.

"We just wanted to adopt again," Carlie Costello said. "It was what was best for our family."

A single email stopped that hope dead in its tracks.

Independent Adoption Center declared bankruptcy and shuttered offices nationwide Tuesday, adding in a news release that a radical imbalance of supply and demand -- more parents than ever now want to adopt, but fewer birth mothers want to surrender their children -- had forced them to close.

"While we have striven to find financial solutions, we have come to the end of the rope and are declaring bankruptcy," the agency said in a news release.

Adoption is never a sure thing, Carlie Costello said Tuesday, but Independent Adoption Center’s sudden closure leaves her family’s future even more uncertain than it had been before.

"We would like to move forward, but how do you move forward (believing) that this isn’t going to happen again?" she said. "How do you trust another agency or trust another person with your money, with your everything?"

Her husband, Billy, felt that heartbreak, too -- both for his own family and for the countless others who were working on adoptions through the agency.

"Even though it’s difficult for us, I’m sure there are other families and individuals in even worse situations that are in the process or in the middle of adopting, and now they’re left without the resources to complete an adoption," he said.

He said he hoped his family could recover some of the money they had invested in their second adoption process and potentially start over again.

In 2014, the Costellos wrote in their letter to prospective birth mothers that they couldn’t wait to expand their family.

Now, although it hurts, they and other families will have to do just that.