Why do you think that someone has access to all of these things?
Some of these things, such as viewing text messages, phone calls, and GPS locations, can be done if you have someone's Google account ID and password (which would apply since this is an Android device). This would also allow them to review your photos that are saved to the cloud, but it would not allow the camera or mic to be remotely accessed. That would require some sort of spyware be installed on your device.
You can check the IP address of the last 10 logins on your Gmail account. This would at least narrow it down and show that someone else has access, and you could contact the police with this information if you truly believe that you are being stalked. Note however, If they use a VPN, it will hide their actual IP address. Click on the Details link next to the last account activity line at the bottom of a Gmail page to review this info.
You can also go to https://myaccount.google.com/security and check under Device Activity and Notifications. This will show you the devices that have recently accessed your account and possibly their location. You can also remove any unauthorized device from your account, but if someone has your login info it really won't help.
There are two steps you should take to eliminate this concern:
1. Change your Google password and enable 2-factor authentication. This will prevent someone from accessing your Google account without your authorization. You can do this via the link I provided above.
2. Perform a factory reset on your phone to ensure that any spyware is removed.