First, you'll need to make sure the cable is the problem. To do this, unscrew the little plates covering the spot the cables plug into, take the cable out, and test it in a USB port you know works (such as in your computer). If the cable can still charge a phone, then the port is the problem.
If the cable is the issue, you can simply order another from Chargebar's website, or for more value, pick up a cable pack.
Here's a simple video to help you change your cables.