A Brooklyn man saved a sick puppy and then launched an online campaign to help pay its vet bills — only to be slammed as a “scammer” by barking-mad neighbors, he said Wednesday.

“The whole thing went off the rails … I was accused of trying to commit fraud,” Luke Perrin, 38, of Carrol Gardens, told The Post. “It blew my mind.”

Perrin was walking to work Monday morning when he spotted an adorable 5-month-old yellow lab tied to a street sign at Carroll and Nevins streets near Park Slope, he said.

A crowd had formed around the abandoned pup.

Perrin soon took the hungry pooch to his office, a few blocks away at Square Design, where co-workers named him Monte, after a restaurant near where he was found.

But after the dog gobbled down food and water, he began vomiting profusely. “Something was wrong,” Perrin said.

A vet diagnosed the animal with gastric dilation and volvulus syndrome, which called for a pricey surgery, he said.

“We started to realize it was going to cost us a lot of money get this little pooch back on his feet again,” Perrin said. “So we started a GoFundMe site to help pay for it.”

The campaign page, which has a goal of raising $6,000, says, “All proceeds will be used for surgery at VERG Brooklyn,” with leftovers “donated to the Humane Society.”

But when some people saw a link to it on the neighborhood-centric app Nextdoor, they tore into Perrin, calling him a fraudster, he said.

“They started to accuse me of running a scam, and they posted a link to an article about the [New Jersey] couple that pulled the scam with the homeless guy,” he said.

“It was ridiculous,” he said. “Now this poor dog was having to deal with pretentious Park Slope BS.”

As a response, he posted a copy of the vet bill in the thread — but some folks refused to back down, said Perrin.

“I totally understand a healthy dose of skepticism,” he said. “But even after I started to produce records, they kept the fight going. They didn’t want to get egg on their face.”

He added, “My intention is not to rip anybody off. If you don’t believe me, you can come by my shop and meet me.”

Ultimately, he suspects the dog owners knew Monte was sick “and didn’t want to pay his bill, so they dropped him off in a wealthy neighborhood,” he said.

Monte’s campaign has since gained steam, and had earned nearly $4,000 Wednesday. The pup may have already found a home upstate, and will likely be just fine.

“He is expected to make a full recovery,” Perrin said. “It turns out there are a lot of animal lovers out there who just want to help save a dog.”