What can I do with a microchipped cat?

[Carmencatp]

Hi everyone.
This is a two year story and it's not finished! I need help!

Two years ago a lovely male cat came to our garden and started to be around. I feed him and let him be overnight during the winter time and all the rainy days.

He came injured and I take care of him (I did video calls with my sister she's a vet on Spain)
I put him flea treatments because I saw he had lots, he was really skinny the first time I saw him. Now he is in 13'22 pounds.

Once we asked our landlord permission to have a pet, we took him to the vet to check if he had a microchip, and, he had one.

We contacted with the owners and give him back, they lived just five doors down, and change the contact information just in case the cat came back again.
Then it's when everything gets more complicated.

At the beginning I text them every time the cat came to my house, but after no receiving any answers I stopped. We are talking about a daily message.
They text me if they don't see the cat, a few times during 2018 or asking me for other cats they don't saw for a long time (it seems I am a cat kidnapper for them), they had seven cats.

This last Christmas I went back to Spain to see the family and they asked my if I could let the cat go, when I told them I wasn't in the UK, they asked me: and who is taking care of him? I get shocked. I answered on the most politely way, even I was really cross.

Since then the cat spends all the nights in my house and they doesn't text me or show any interest on the cat.

With this lockdown situation, working from home I observed the cat just go out early in the morning but later if he asks me to go out stays around, I can see him from my window.

How can I approach to the owners or the RSPCA so I can keep the animal on my own name, because it's microchipped, and I really want to take him with me once I go back to Spain forever next year.

Thank you so much for the answers and apologies for my poor English.

Offer to buy it off them?

I am not sure I it will work, because when I contacted them the first time to return them the cat, they were really insistent on having him ASAP and told me how much they love him. And they told me that story of neighbors stealing their cats... ( If they doesn't take care of them and the cats are not microchipped this things happen...)

They don't care about the animals but at the same time they want to keep them because it's theirs... It's frustrating

It sounds like you're asking for advice on how to steal your neighbours' cat legally. Cats with outside access wander. They often have several friendly houses they call on, a bit like people with pubs. You can't take your neighbours' cat. They obviously care for him. They've had him microchipped. You shouldn't really be keeping him in overnight. But if you're convinced your version is correct then as pp suggest offer to buy him. And if they say "no", accept that. He's their cat.

I think I’d offer to buy him too. They clearly don’t care to actually responsibly care for him if he was flea/ridden and in a poor state.

Alternatively you could offer to take care of all vets bills / treatments / food etc. if they agree to transfer the microchip ownership. But I suspect cold hard cash would work better with people like this.

That's the kind of comment I had on my mind all the time. Am I stealing their cat? It's this ok? I mean, I can have the thought that they don't care about him, but how can I know this?

Thank you all of you for your advice, I will try first to talk with the owners to know if he goes regularly to the house, and if it's a no, I will tell them it seems he moved to my house by his own and what can we do.

They may be his owners, but it seems like they're not taking care of him. They know that he's spending most of his time with you, otherwise they wouldn't have called you whilst you were in Spain and then seem shocked when they didn't then know where he was. I'd offer to take him in completely and if they agree, get proof that they've changed the microchip details to yours. I think it costs £10 to do this, so offer to pay for it. If they say no, they don't want to give him to you, then offer to buy him, not nice I know, but see if that changes their minds. Make sure you get the new microchip certificate.