I have duplicate contacts and I'm not able to delete them.

You can delete duplicate contacts on the Contacts page (top right nav bar). 

The system will not allow you to delete any contacts associated with an open ENERGY STAR Certification Application (as the Primary Contact, Signatory, or Licensed Professional ) or an open Data Request. You can delete these contacts after the application is closed.

As a work-around to temporarily hide these contacts, we suggest you add a "ZZ" before the first name of the person (ex: "ZZ John") so that that contact moves to the bottom of the list and you will know not to select them again. Once the application or data request are closed, you'll be able to delete the contact.