Site Security fix

I recently migrated my domain and hosting from bluehost after several series of brutforce attempt on my site, thinking that Godaddy would resolve the entire security issues. However, i have migrated the domain and hosting from bluehost to godaddy VPS account but still have same issue. It is a WP site, and i have noticed that some basic members capability role has been changed to administrator which i never did by myself. Unusual activities are being carried out on it on the site. The Site keep going down while my word fence plugin keep telling me that the site has been attempted to access via numerous unregistered usernames. The site goes down every Saturday and Sunday that i normally host my weekly webinars. Some times it says that i am out of resources usage which i know it isn't true. I need your help in eliminating all infection or threat to my site and then correct it to work functionally and also help to secure it with all of the best Ddos security sysem on earth. Let me know what you can do for me.