AWS EC2 instance not accessible via public IP address

Is internet gateway associated with VPC, if yes then, is IGW entry added to subnet route table, where the ec2 is launched.

Since you already mentioned security group is fine, so I'd check above two things first and make sure that those are in place. Make sure security group has custom TCP rule for that defined port for your ip/everyone(based on your requirement).

Additionally take a look at this re:Post thread.