Welcome to the forums. Chances of this happening are extremely slim. However, I would operate under the assumption that this has been done. You have some options.
1. Non reset option:
1a. Remove any apps that are in your app drawer that you don't recall adding.
1b. Change any passwords on sites you normally use, including your Gmail account.
The above should get rid of whoever may be on the device. It also will force you to change your passwords as anything connected on that phone may be compromised. Changing your passwords frequently isn't a bad idea to begin with. It's not fun, but sometimes necessary.
2a. This might take some time, as resets aren't fun. You would have to set up your phone all over again. Back up any data you don't want to lose. The upside is where the first option might miss something in place, a reset should get it. Once the reset is done, I would NOT automatically download all your apps over again. Only install the ones you want/need. Once the reset is done, change your GMail account password and all other ones as well.
While the above advice might be helpful, if you have a keylogger sending packets to the hacker constantly, it won't solve the problem. He'll know your new stuff too.
First, enable 2 factor authentication.
Then, go to a pc, log in to your Google account, and check all the settings and permissions. Go to the playstore from the desktop and add a pass code for downloads.
Change your password after your sure you are free of malware.
If you were hacked, you need to do more than just wipe the phone.