Actually all the tracking numbers are unique, but the truth is that all tracking numbers are stored in one database. If you have troubles with contacting DHL directly, you may use
package tracker to find out your delivery. When I had the same situation as you, the local logistics company denied my complaints about the lost delivery, so I immediately used this tracker to figure out what happened. Finally, my package was delayed somewhere in China and I was redirected to my actual address. Pretty messy story.