And where is that quote from? Because it's not in any of the OP's posts, it's almost like you've made it up to fit a narrative of your own making.
Here
So.... logged into Facebook for the first time in a while and at the top its asked me if i wanted to claim an interior design business Facebook page as mine.
Out of curiosity I clicked yes and clicked through a few screens and now I have control of the page and have the business owners email, private mobile and their address
1st bolded section is Facebook asking: "Is this your business?". i.e. "Are you the business owner?", i.e. "Is this you?"
2nd bolded section is OP saying "Yes"
It's not exactly crime of the century, and the vast majority of the culpability lies with Facebook, but it's still fraud. It's a bit like if you are walking down the street and somebody taps you on the shoulder and asks "Did you drop this?" whilst holding up somebody else's wallet and you say "Yes". Except in this case you can't then notice your mistake and go "actually no, sorry, looks a bit like my wallet but on closer inspection I realise it isn't, I'll hand it in to lost property"
OP should contact the business owner, explain what happened and suggest splitting any compensation from Facebook for the data breach.