Amazon EC2, Elastic IP, NAT and license problem

Hi, I'm build Centos EC2 instance on AWS. On clean installation I was installed CPanel. I used few days of trial period before I bought license. Right before I bought license I was change IP address of EC2 instance on Elastic permanent IP. License was bought for that permanent IP but for hostname was entered amazon private dns. One day after that I was change hostname with some my domain on example: srv.mydomain.com Everything works fine few days when I decide to increase instance resource and build new instance from this old. I was increased resource and point same Elastic IP for which I bought license but I can see only message for every domain on WHM that IP is misconfigured or then DNS problem... I know that WHM on EC2 use NAT, and NAT is enabled from start by default on WHM. When I back again on my "old" first instance which I created, everything worked. One think present here which maybe has problem and I need confirmation for that. In moment when I was built and start that new larger instance, old instance was worked too but on changed, different IP address. Could be a problem in that ?