We are currently using Stackoverflow Enterprise version which our IT Engineers use to ask questions from internal experts. I am wondering if there has been any instances where such content was successfully migrated to Discourse?
Also, how do I engage with the Discourse sales team? I checked the website and could not find this information.
Hello and welcome @Arvinder_Chopra 
If you’re looking for an Enterprise plan there’s a contact form on the Discourse pricing | Discourse - Civilized Discussion page, but for all other plans you can spin up a free trial from there and ask any questions to team@discourse.org 
We can build a custom importer for Stack Overflow Enterprise as part of your enterprise hosting package with us. Since Stack Overflow Enterprise allows exporting content to JSON in the admin settings it shouldn’t be a problem to obtain the whole data on your current instance to be imported into Discourse.
Yes, I am aware of a (non-public) instance where this has been accomplished. The importer was made by a client and is not open source, but it can certainly be done.