When I reached officer rank I had to kill 1500 zombies total, get 1 crow mounts and upgrade mount duration...

When I reached officer rank I had to kill 1500 zombies total, get 1 crow mounts and upgrade mount duration. I noticed that as I went through the runs my zombie kill count wasn't increasing and neither was the get 1 crow flight achievement but the upgrade worked. The only thing I can think of doing to try to fix it, is to kill 1500 zombies in 1 run and get a crow mount. This task seems almost impossible as I got to 150k score with only 1100 zombie kills and I killed pretty much every single zombie possible using the shelby to get all the lanes. I can't seem to fix this glitch was wondering if you guys had a fix?