Can't upload any images or add links in posts

I am trying to get my blog up and running but can’t upload any images, change the header, or even add any links into posts.

This is my website: https://www.reinventionofnormal.com

For example when trying to change the header, I go into the appearance area and click into the header area, click “select image” and nothing happens. The “Select Image” button highlights but nothing pops up, in fact nothing at all happens.

The same thing happens when in a new post, I can’t insert any media or add any links.

The theme installed is Rosemary by Solopine, and at the moment I am stuck with their header since I can’t change it to my own one. I’ve been in contact with Solopine and their reply was this:

The issue with your logo image is very strange. I believe it is related to a larger issue of uploading images to your WordPress installation in general. I tried several times to upload an image to your Media Library and it would appear to be successful, though on refreshing the library nothing would be there. I also switched over to the default WP “Twentyfifteen” theme and experienced the same issue there as well, making me think it’s a WP installation problem.

I have also contacted my hosting provider (HostBig) who also reckon there is nothing wrong and asked me to send a screen shot but there is literally nothing to send a screenshot of since the problem is that nothing is happening. And to be honest, their support team have not been very helpful at all.

I had quite a lot of trouble uploading wordpress in the first place so I am hesitant to uninstall and reinstall again since it took so long/so many attempts. But if this is the only solutions then I would appreciate it if someone could point me in the direction of instructions to do this!

Or if anyone has any other solutions to this I would be most grateful!

Thanks so much,
Juliet