Setting up reverse DNS on an ISPConfig 3 server
I have had the same problem.
PTR record is controlled by your ISP and it cannot be controlled by your DNS records.
I got it changed from my ISP, which should resolve to my domain.
with my experience I am sure, there is no other way, than to request your internet service provider to make the necessary changes in your PTR record.
The same is only possible if you have a STATIC IP for your internet service.