If I can decode correctly what the replies you're getting in those other forums, it's completely nonsense (unless you jailbroke your iPhone in which case all sorts of bad things could be possible). They are not controlling your iPhone, an iPhone is not "built for remote connections", and someone gaining access to it remotely without your explicit agreement is highly unlikely if not actually impossible. Nor can your iPhone be cloned or used to access other devices.
More likely is that your ex has access to your Apple Account and is able to get to your synced data that way. See:
If you think your Apple Account has been compromised - Apple Support
If you still think your iPhone itself has been compromised, post back and tell us what exactly is leading you to believe that it is.
Regards.