No way the pads should need replacing at that point.
Either theres something mechanically wrong with the brakes, or the sensor is funked. You should be able to look at the actual caliper and see how much pad is remaining.
The rears on my last car lasted 95,000 miles, and still had 2-4mm of pad left.
Current: '15 M235i Vert
Previous: '13 335i, '08 TL-S, '00 Corvette