2.0.0.GA is somewhat old.
There was a bug with Topics on the Resource Adapter. You should upgrade to 2.1.2 (or 2.1.3 coming soon).
This question is very hard to answer since so little information is given.
Messages will be redelivered if they're not acked. When acking happens depends on the application and it's configuration.
OK, thanks. I will upgrade to the latest version. If that still does not appear to work, I will provide more information.