I noticed you did not specify calling conventions. Here is what the manual says about that.
Calling C Programs from COBOL Programs:
When the calling conventions is omitted, its assumed COBOL calling conventions.
Have you tried "CALL 'PGM' USING C LINKAGE" or
"CALL 'PGM' USING STDCALL LINKAGE".
I have not ever tried this myself however, thought this information may be helpful. Goodluck.
etom