I thought of another possible problem.
I always thought in the explanation of how to report contacts there may be a language issue.
So to clarify: the direction you plug into the TDC is the
direction of the convoy not your course.
Incidentally, one mistake I make regularly is that I look around through the UZO identifying ships. Then I send the contact report before checking where I have set the UZO, thus giving the wrong direction for the convoy. Something to keep in mind.
I expect you are probably doing this right, but this could lead to the wolfpack showing up, just completely in the wrong place.