Reverse DNS is not updating

Hello everyone,
I know it will probably be a mistake that I made but the reverse DNS that I set in the network configurations of my Linode is not resolving properly. I set the reverse DNS of the IP 194.233.170.192 to postatna.com. When I query the PTR record from the ns.postatna.com DNS server, the domain name is returned correctly, which indicates that the DNS server is configured correctly. However, when I query the PTR record from other DNS servers, e.g. 8.8.8.8, I receive the domain not found error. I waited for three days for the record to propagate throughout DNS servers but still not resolving correctly!
Could anyone please suggest a solution to this problem or a troubleshooting procedure?
Thanks in advance!