Contacts are still syncing from my mums phone to mine
I have recently brought a new phone and my mum is now using my old one. I have logged out of my iCloud on my old phone so that my mum can log into her iCloud. We are both logged into different iClouds and on separate phones but the contacts still get synced to each mobile. I have checked that we don't have each others devices on each others iCloud, so I'm unsure of what else to do to stop the contacts syncing onto each others phone? Any suggestions please?
iPhone XS