If this is a WSFC, then you should connect to the SQL Cluster Name - the one defined during SQL 2016 setup.
Because you have a named instance, it would by ClusterName\mssqlcluster2,port to connect from SSMS.

If you can't connect like this, look at the Windows firewall on the server.  If you're on the same domain as the servers, then try turning off that firewall.

I guess one question should be if the cluster ever worked, meaning allowed connection to it from SSMS, or if it just stopped working.  If it never worked, your DBA should be able to help get the initial configuration done.