For starters, it's hard to hack into someone else's Android phone. Not impossible, but not something an average user could do. So let's look at a couple of your issues.
Wi-Fi and Bluetooth can be turned on and off automatically based on your location, as a way to automate things. I.e. You get home and it turns Wi-Fi on so you don't have to. If you go out, it can turn Wi-Fi off for you, and activate Bluetooth to connect to your car. So go through your settings and look to see if anything like that is set up.
Those unknown numbers calling you are most likely nothing more than spam calls. Robo-spam calls are running rampant right now. Even if you are on a "do not call" list, these scammers don't care about that and will call anyway.
Has your ex ever had possession of your phone? And what do you mean by "tapping" it? Please register an account here to answer and also help us figure out what's going on exactly.
If you still really think you have been hacked, then I would just go the nuclear route. Factory reset the phone (make sure you know your Google login and password, as you will need this to set it up again) to wipe any spy programs from your phone. Next, get a password manager and give it a strong master password that you can remember (I personally recommend Last Pass). Use the password manager to create entries and help you go through all of your accounts to change passwords, giving them all unique, random, strong passwords. While you're at it, turn on two factor authentication where possible.
Hacking these days doesn't have to mean actively interacting with your phone. If they have your login info for Google, Facebook, and other big name accounts, they can wreak havoc from anywhere because so much of our info is now cloud based and synced in real time.