Original Owner? Wants Cat Back

Hello, kind of a long story here

So a few months ago while sitting outside, a cat came up to me. He looked skinny, fur all dirty, he wasn’t neutered, messed up, and just generally uncared for. Even though I’m allergic to cats, I still took him in because it was just too sad to look at. We cleaned him up, took him to the vet that night, got him scanned for a chip (he did not have one) and did everything correctly.

After taking him there, feeding him, we let him out again, but then he came back 4 times! So at that point we decided we were going to take care of the cat until we found its owner. 2-3 weeks went by of looking for the owner, and there was nothing. We posted on social media, put flyers up, and still nothing. So after that we decided to keep the cat, took him to the vet, got his shots, chipped him etc. and formally adopted him.

We’ve now had this cat for around 4 months, with him being still under a year old at around 10 months old.

The other day he got out with a freak accident with the wind from a big storm blowing the door open in the middle of the night. We posted everywhere and actively looked for him all day. We luckily eventually found him, but later on in the day, I got a text from a random number claiming the cat was theirs! They sent a bunch of pictures, and asked to come meet the cat in person. I told them I felt uncomfortable with the situation since it was a random number and thought it would end there. They then threatened me saying horrible things were going to happen to my family and that I stole the cat etc.

So I was wondering, what’s the process here regarding my kitty? I obviously want to keep him, he was in bad condition, and even the vet said he was 100 percent a stray or just totally uncared for. The microchip is in my name, and I also have vet bills and records from when I first got him.

Please help, I’m freaking out about losing my baby

Location: South Carolina