Disclaimer: I'm a web designer, which is only tangentially related to cover design.
Mostly, I think the issue with your cover is it doesn't fit your story. From your blurb, I got the impression you wrote a thriller with a lot of tension, and that's not reflected at all in the cover.
The colors are neutral and toned down, the typography is simple, the illustration is simply characters standing. There's no sense of threat. I don't get a "could cost them their lives" vibe from it.
The white background gives an amateurish impression to me. White covers are very uncommon, and you need a top-notch design to make them work. With the stock image silhouettes, it doesn't really work here.
If you have the money, I would definitely redo the cover, but maybe not right now. Most self-published writers see an uptick in sales when they publish a new book, so you could wait for your next book to republish this one with a new cover.
Edit: just noticed you made the cover yourself, so I wanted to add it's very good for amateur work. It looks very clean.