Help Pls: Audio Download Problem – WordPress or Theme Issue?

So here’s my problem in a nutshell:

I’ve created a website for a client using the Mission CrowdFunding Theme (think it’s a child theme of Twenty Thirteen). All went well until I discovered that the feature for downloading sermon mp3 files (NOT a plugin, just a feature native to the theme) which I’d uploaded to the WP media folder didn’t work; I received the following error:

NOT ACCEPTABLE!
An appropriate representation of the requested source could not be found on this server. This error was generated by Mod_Security.

Thinking it was a server issue, I contacted the hosting provider, hoping there was a setting they could enable so that downloads from the site could be whitelisted. After some delay (they’d never encountered this issue before), they did a bit of digging and determined that there was nothing to whitelist; rather the problem was the format of the mp3 url – it contained a .php extension that was a security risk.

The thing is though, that the mp3 url that I attached after uploading it to the media folder DOESN’T contain that extension; .php only becomes visible when we attempt to download the file on the front end.

For example, here’s the url I attached:
https://bethanycovenantalive.org/wp-content/uploads/2015/07/Why-We-Worship-on-the-Sabbat.mp3

But here’s the url that shows up in the address bar when a download attempt is made, triggering the error:
https://bethanycovenantalive.org/wp-content/themes/mission/download.php?type=../../../wp-content/uploads/2015/07/Why-We-Worship-on-the-Sabbat.mp3

I tried to get around this problem by using FTP to create a folder at the root level and uploading that way. No luck.

I even contacted the theme’s developer who advised me that it was a hosting issue and that I should contact my provider. Already did, and received the above information about the url format, so no help.

Does this seem like a WordPress problem, and if so, how do I resolve it?? Or does it seem, as I suspect, like a THEME issue? Perhaps a problem with the Download Audio favicon on the back end?? In which case am I screwed for help? No one I’ve spoken to seems to have encountered this issue before.

HELP!!