I also faced the same problem with the E3531 and I found the best solution
*IMPORTANT DO THIS WHOLE STEP ON THAT SAME PC USING WiFi so that the inbuilt modem driver of the PC remains busy otherwise inbuilt microsoft's modem driver will attach itself to the huawei E3531*
STEP 1: Download a customized version of mobile partner from this page .
STEP 2: Extract and install on your PC
STEP 3: Now connect your HUAWEI E3531 (you should listen USB insertion windows sound)
STEP 4: Now close the customized version of mobile partner and install from the USB driver itself
you are done!
It worked on windows 8.1 pro didn't tried on windows 10 but it should work on 10 too.