Try running MSD.EXE, the old Microsoft DiagnosticS program included with trueDOS since (I think) 5.0
Find it at
http://www.simtel.net/pub/pd/47978.html if you don't have it.
That should tell you quite a bit about what what actually is there and what DOS thinks is there, particularly ports.
COMSTAT.COM available in comstat.zip from
ftp://files.chatnfiles.com/Simtel/DISC2/SYSINFO/ gives more detailed & accurate but rather stark and techie info. about your COM port status.