Mr-potatoL There are lots of ways to be tracked beyond just a VPN, security is about layering. A VPN is one step of multiple steps to hardening. There are firewalls, browsers, tightening general settings, avoiding certain software all together, using PII to pay for services, fingerprinting, where you ship to, etc, etc. You're on the right track, so I recommend those books above which are specific to mobile and VPN's. If you're more generally interested in privacy, he has a good book on that too on his website and Amazon. There are helpful people here as well as some YTers (Naomi brockwell for example).
This type of stuff takes a lot of time and research, it's a marathon not a sprint so don't get discouraged.