redirected to different site and receiving a 404 error

I seemed to start having problems after I updated the Bulletproof Security plugin on my site. First, I got a 403 and then a 500 error, which my hosting company was able to resolve. Now when I log into my site, if I try to access my pages from the dashboard or click on the different page tabs from the homepage, I get redirected to a site I’ve never seen before and get a message at the top saying there’s a 404 error. I called the hosting company, and they told me it was an architectural problem in WordPress, and that I would need to contact support in this forum. What do I need to do to correct the problem?