Please suggest a fix for my worthless site

Please guys I need your help. I have tried my best for weeks to fix this issue all to no avail.
My wordpress site is automatically changing my username and password only. I use Securi security plugin with no success. Please I need contributions on how to fix this nightmare on my newsite. You can check up the site on techguides(dot)com(dot)ng

scan your whole website might be some hidden script.

Login to your C-Panel
Go to WordPress plugins folder
Rearrange the plugins folder list from modified tab
Delete the lastly installed plugins
If its not successful

Try this last one. but before you do. Make sure you have you site content backup. Delete the third party plugins and check it.

First scan it through or or

It will show the hidden scripts - remove those scripts and plugins

The error occurs because you might be using free sources or nulled themes.