Infinite Redirect Loop after moving blog

Help! I need this resolved ASAP as this is a production blog – any help would be appreciated!

My blog was set up at https://myaccount.host.com/blog, but it was actually pointed to by https://www.company.com/blog. In other words, my “WordPress Address (URL)” was set to the former, my “Site Address (URL)” to the latter.

I need to convert this to a multisite setup with domain mapping, but unfortunately this required me to move the physical location of my blog from https://myaccount.host.com/blog to https://myaccount.host.com/.

This was easy enough to do: I worked with my host to move the blog from the “blog” subdirectory to the root folder. Then I contacted my IT department and they pointed https://www.company.com/blog to https://myaccount.host.com instead of https://myaccount.host.com/blog.

In WordPress, I was able to change my “WordPress Address (URL)” to https://myaccount.host.com instead of https://myaccount.host.com/blog. So far, so good – I have access to the backoffice.

Unfortunately, the front end results in an infinite redirect loop. The ONLY way I can get it to stop is to change the “Site Address (URL)” to match the “WordPress Address (URL)”, which is https://myaccount.host.com.

However, if I do this, when a customer visits https://www.company.com/blog, they are redirected to the ugly host address, https://myaccount.host.com.” This also kills our SEO.

Ultimately, I need this to work EXACTLY as before, where a customer views our blog through https://www.company.com/blog, but the blog needs to be in the root directory of my hosting account instead of the /blog subdirectory.

I hope that was reasonably clear – please help!

PS – I haven’t even starting setting up multisite yet – all these problems are on a simple installation.