Why wont my "Clear Cache" work?

This may because of one of two reasons-

1. Your phone clears its cache without displaying a pop-up message saying that it completed the task. Some phones are like this.
2. Some apps are programmed to not clear cached information that is necessary to receive the services you want to use.

A good way to reset your phone back to its original state is to perform a full factory reset. This will clear the phone’s cache, remove any malware, and perform any needed updates at the same time. You can do this in your phone’s Settings.