Keep in mind that there corporations that put millions of dollars of resources into locking down their online presence, as do entire nations, and the end result is always dependent more on luck and happenstance that some exploit or compromise gets revealed.
There are unavoidable weak spots in both hardware and software and some people just aren't able to comprehend just how complex and involved any computerized device is inside. We interact with them by pushing a button or tapping on an icon, and each time that happens it might involve literally thousands of lines of code to be processed (software) to trigger thousands of interconnected components (hardware) to do some function. That all happens with milliseconds and most of us don't even appreciate just how complicated any smartphone is inside.
To answer your question directly though, no, there is no way to make your phone 100% 'hack proof'. You could never turn it on and that would be the only way to always keep it safe and secure, but that also negates any reason to even have it. Smartphones are by design intended to be interactive devices.
From your description, the problems you're having sound be less about your phone and more about one or more of the online services you're using have been compromised. A likely target would be your Google account. Actual 'hacks' into any smartphone don't just happen spontaneously, the user is the weak link and it's all the online services that we set up on our phones that allow problems to get access.
You might want to try
-- Back up all your data to a PC and thoroughly scan all the backup data with a trusted, brand-name anti-virus/anti-malware utility
-- So a Factory Reset of the your phone
-- Before going through the data restore, reset all the passwords for all the online services you had previously set up on your phone. If it was compromised by some kind of keylogger malware, the a-holes have your old passwords. With new passwords you'll need to re-authenticate those apps again, notably the Google account your phone was tied to will need the new 'clean' password.
Reset the passwords to all the online services you have set up on your phone.