Let see. I had to refresh my memory on SVG, I haven't used it much these years.
From what I found today, it seems that if you specify dimension of objects without units, they have a fixed size (in pixels, I think). Apparently, then, there is no way to resize them when you resize the SVG (it only change the viewport/canvas size).
Unless, as pointed out, you specify the size of the SVG in percentage OR specify a viewBox (eg. viewBox="0 0 600 500").
Now, if you have no way to change the exported SVG, you are out of luck, I fear. What library do you use?