Well that is a security problem waiting to happen. Running windows RDP over the internet is insecure enough, but leaving firewall completely down for an internet facing server is like taping the keys of your car to the outside driver window.
Since you said their support will not go in and disable the firewall for you then you are going to have to either restore from a backup (if this is even an option, and if a backup was actually ever made), or go through whatever process you need to do to completely wipe the server and start over.
After you do get yourself back up and running you need to create a rule to allow RDP instead of leaving the firewall off. You dont remove the doors because you dont have a key to the locks that came on the house, you replace the locks.
Frankly you should be using VNC or something like Teamviewer for remote connection anyways as windows RDP is highly insecure.