Happened to a cat I had years ago when a neighbour who kept feeding him refused to when I asked her to stop. She said the cat spent more time at her place so it was now her cat !
She lived next door and spoilt it rotten. I wasn't going to get in to a 'treats war' with her, so let it be and cat came back of its own accord. When neighbour asked me to stop letting cat in my house I said, "soends more time at my house now, so MY cat". Catnip played a part if I'm honest, I grew kilos of the stuff.