Erm.....if I understand correctly I think you're looking at this from the wrong perspective.
I don't believe this is a SoapUI issue.
SoapUI is only going to be able to provide any workable status response if the endpoint you have specified is correct. If it is correct then you need to consider logs, look at the RAW request and response etc. to work out what's going on.
SoapUI nor any tool I wouldn't have thought would be able to give you info indicating what is wrong with your endpoint if it is incorrect.
I'd double and triple check the endpoint is correct relative to what the client provided (as well as the security/authorization options) and if you're duplicating what was supplied, you need to go back to the client who setup the endpoint for you to ensure the endpoint is correct, message body is correct (if a POST/PATCH etc.) and the security creds/Authorization settings are correct.
I'd suggest checking your network settings - are you behind a firewall? can you only connect to the endpoint from within a specific domain? etc. - but I'd expect that you'd get something in your logs (destination host unreachable or permission denied etc.) if this was the case - hence the reason I'm leaning towards confirming the endpoint details with the 3rd party (but double check your settings first though!)
Perhaps someone else has some whizzy ideas to help - but I've got nothing!