ATLANTA — For 34 years, Robert Thompson Jr. had been a business and labor lawyer — as was his father before him — defending corporations and financial institutions and even serving on several banks’ boards of directors.

But something happened to him two and half years ago that changed his entire practice. Now, he challenges banks and financial institutions in court, accusing them of wrongful foreclosure and outright fraud on behalf of individuals who are a step away from losing their homes.

The turning point for Thompson came at Christmastime 2009. His mortgage servicer — with whom he had been embroiled in disputes over what he said were misapplied or lost checks, late fees for payments that had been made on time, unnecessary insurance costs and double billings for taxes — moved to foreclose on his home.

“I was a single father with three young children living with me in that house,” the silver-haired Thompson said during an interview in his Buckhead Thompson Law Group office filled with books about the financial industry and the economic crisis. “It was very upsetting.”

But, he added, “I was the wrong person to pick on about injunctions and bank law.”

On Dec. 28, 2009, he went before Fulton County Superior Court Judge John Goger, asking for an order enjoining the mortgage company from proceeding with the foreclosure. The judge’s first question was, “How much do you owe?” Thompson recalled.

“I told him I didn’t owe anything, that my payments had all been made on time, and that in fact they owed me more than $50,000 in overpayments and mystery fees,” Thompson recalled.

“Can you prove it?” the judge asked.

Thompson recalled he pointed the judge to canceled checks and FedEx receipts, and the judge granted Thompson’s injunction. Thompson filed a lawsuit against his loan servicer for mortgage fraud and abuse, wrongful foreclosure, unjust enrichment, breach of contract, conversion, misrepresentation, defamation, libel and deceit.

“People started talking about it,” Thompson said. “I thought it was just me, but then people started calling saying they had the same problem and wanting to know if I could help them.”

Now, Thompson is a man obsessed. And he said he’s had success halting foreclosures — but acknowledged securing such an injunction for a client is only the first step.

Thompson said he still has new clients coming to his office daily. Most don’t have the exact situation as his, where the payments were current but not applied to the account. The biggest percentage, he said, are struggling because of a loss of income and are seeking loan modifications to make payments more manageable, but were told by their mortgage holder they weren’t eligible either because they weren’t behind or far enough behind.

Thompson said being behind on mortgage payments isn’t a requirement of federally funded modification programs. But, on the assumption that it was, he said, his clients missed payments in hopes of qualifying for modifications, then found themselves in foreclosure with their lender refusing to accept more payments. Thompson calls that being “lured into default.”

Out of hundreds of cases he’s reviewed in the past two and a half years, he said, there wasn’t a single one where he didn’t find fraud or at least errors in the records. So far, he said, he has not yet been able to say to a homeowner, “I can’t help you because the bank did everything right.”

Bank representatives say it’s absurd to suggest banks want to foreclose if there are other options. They admit some paperwork mistakes happen but suggest it’s not right to make those a basis for loan forgiveness.

Meanwhile, Thompson is ordering up forensic audits — at a minimum of $1,000 each — to ferret out problems so that he can go to court to block foreclosures. A forensic auditing company analyzes the loan activity and tracks the transfers of deed and title as the loan has been sold by one financial company to another — and sometimes to several others.