To get complaintant letter through rti

Hello Experts, I am constructing a house in my native. Recently, one person complained to the corporation that our house has certain deviation/violation from the approved plan. Corporation in turn sent a notice to us. In the notice, under the reference section, person who gave the complaint name was mentioned. We responded to the corporation notice. We also filed an RTI to know the contents of complaint letter. But the public information officer sent a letter to the complaintant asking for his consent, complaintant rejected, hence PIO too rejected stating this comes under third party privacy. My Question is, we are the affected party and in the notice the complaintant name is clearly given. In such circumstances, how the complaintant can be a third party person ?. Is PIO right in his approach ? Is there any other options available to get the content of complaint letter ? Thank you. Regards, Sat Re