This is possible if your partner has access to your devices and the know how.
You can run security scans on the phone which one is built in the phone and some are available via the Playstore.
Other options are to factory reset and don't use any back ups.
Start from fresh.
Speak to your network and any relevant authorities if you feel your information has been breached i.e banking apps etc.
Google Search about how a phone is cloned.
If I can be of any further help then please don't hesitate. Take care. 😎
Daily Driver > Samsung Galaxy s²⁵ Ultra 512Gb ~ Titanium Black.
The advice I offer is my own and does not represent Samsung’s position.
I'm here to help. " This is the way. "
