I'll second the advice on calling too loud and gobbler zones.
If a tom can hear you, but doesn't see the "hen" where it's supposed to be, he can hang up. If he's responded to your calling, and then scomes into sight, many guys will just stop calling altogether. Maybe a few soft contented small calls will draw him into range.

Also, you may be near the edge of a larger tom's turf. In that situation, the other gobbler may not want to trespass and get a whuppin from the other tom.