Trouble getting Neighbor Access Form signed

[Chris Nerio]

Hoping to get some help with an issue regarding access to a neighboring property in DC. We have basically completed the permit process to begin rehabbing a row home in DC. In order to complete the rehab we need to extend the neighbors chimney. I have spoken to the neighbor already, who seemed fine with the work, but when I sent him the access form to his property to sign to give us permission he has no longer been responsive. We have tried everything from FB messenger, email, phone, even process server and no luck. 

Does anyone have any other idea on how to get this signature or a way around it? Thank you.