To enable global access to this database, I made its IP global
Don't do that.
Even for experts this is a massive no-no. If you don't even know how to start investigating this them you still have a lot of learning to do.
Additionally, I added a password to my phpMyAdmin
So you didn't just install MySQL, you also installed a webserver, PHP and PHPMyAdmin.
someone is repeatedly deleting the database
Given your description of events this is not surprising.
If you really must expose a host like this, then using MS-Windows is not a good start. It exposes a LOT of attack surface by default and is difficult to automate management.
While this is FAR from an optimal solution, based on a VERY constrained budget and skills, your quickest approach to protecting the service will be to install a vpn server on the host and configure a host firewall to block ALL external traffic apart from:
Whatever protocol you use for remote admin (ssh or RDP over SSL are OK, so is direct console access - if you are using something else, change that NOW).
the VPN end point
BTW if someone can interfere with your data then they could easily have access to the OS - wipe it and start again from scratch.