You're right, they can't talk to anyone without your consent unless you lose capacity, in which case you would be sectioned.
It's probably just concern to get someone to look out for you if you can't do it for yourself.

If they do something you don't like and you want to complain, PALS (patient advice and liaison service) will help you. They're independent and the CMHT have to give you their details if you ask for them. The receptionist can probably give you that information.

I hope you can work it out with your CPN.