There is a certain amount of legitimate paranoia which comes on anyone who is technically competent and starts thinking about security and the systems most people trust without question. This sounds like the place you are now. Once you start thinking about it, it won't go away, and you will learn to manage it.
Don't use the word "they" when you think about who can intercept your calls or hack you. That ways lies unhealthy paranoia, where anyone can start to seem "off" or "acting weird". Even without that bias, bringing up anything that might imply your cell provider not securing their network will confuse a call center employee at best, or put them on "careful what I say" mode because that way lies legal liability for them. Not sure if that's what happened, but it's one explanation.
There definitely exist people and groups in this world that can hack you in a variety of ways: legally (FBI using a warrant), probably legally (NSA without judicial approval), or illegally (criminal hackers). Most likely the first two don't care to attack you, and the latter have no reason to risk performing an attack on you unless you recently made some shady enemies. If you care to do so, you can minimize the number of such groups by using end-to-end encrypted technologies like FaceTime. Google is allegedly working on end-to-end encrypted calls, as well, and has included WebRTC into Chrome. Signal by Open Whisper Systems and Firefox Hello by Mozilla also provide e2e crypto, if you prefer open source things.
Realize that the challenge you're facing is both technical and psychological. Start thinking systematically about security. If you think your phone is hacked, ask "how did it get hacked, and how do I prevent this with my next phone?". Did the OS get rooted, or is it just one of the apps that could be acting weird? Cell phone makers spend a lot of resources securing their manufacturing, hardware, software, and platforms, and it's really expensive and risky to perform an attack on someone who follows best practices.
That said, don't imagine that you can be secure all of your systems against everyone all the time. Angela Merkel can't, and she has way more resources than you do. Security is all about increasing the cost and risk of an attack and decreasing its value, something worth integrating into your lifestyle regardless of whether you're a target now.
Finally, about schizophrenia: there's definitely stigma there. Don't worry about it. Read the DSM  to understand what symptoms drug manufacturers target in their drug trials. The point of the categorization is for medical treatment, not judgement, and it's none of anyone's business except the people who you choose to tell. If your security concerns get so bad that they interfere with your daily life more than you want (i.e. you can't work or have close relationships), get diagnosed and meds to help you get back on track. Based on your writing, it doesn't seem like you're suffering from anything that will require you to be on meds for a long time, even if you choose to use them. A doctor or therapist can be a good advisor in this regard, as can friends or relatives if you can find someone qualified.
Stimulants like Adderall are in some ways the opposite of anti-psychotics, so that definitely won't help you.