There has been a stray cat on my street for a long time. I never knew he was stray until he had a terrible wound to his neck, a burst abscess with skin dangling down off his neck. I assumed he had no owner as nobody was treating this and I saw him several times with the skin still hanging off. I tried to catch him and some weeks later I did, took him to the vet and he was unneutered in tact male covered in fleas. Someone on my street said they would take him in but didn't in the end. I investigated on the local Facebook cat group and turns out that lots of people knew of him, fed him and was a known stray. One woman had taken him to the vets with an infected eye which needed removing. I put a paper collar on him with my details but nobody called.
Last week he came into my house and I picked him up, took him to my mums house as she had spare room for him. He has since been neutered, microchipped and had bloods done. Sadly he has FIV so needs to be kept indoors but has lots of space to live a happy life indoors.
Today two people came to my door and stated they owned him. They said he was a feral cat who they had been feeding for years and had a bed for him in their garage. He had been roaming the area when they moved into the street. They apparently decided not to neuter him, microchip him, basically give him any real care.
They demanded that I get him back from my mums house and return him to them. They admitted that they did not own him but that he just lives in the area.
I explained that due to his FIV diagnosis he needs to be an indoor cat, they clearly didn't understand what that means.
Any advice on what to do?