After a fantastic mission i got 0 ships and no renown!!!! Bug? Any ideas

[VonApist]

Good morning to all!
My first post here, even though I have been playing the game for quite some time with a fair degree of realism ( in only have external cameras on, stabilisation ON and the WTO to provide me with the firing solution). its the first time i encounter this problem and it was really a spoiler!! It just send a really good first patrol down the drain!. Let me explain :
I decided to start over my carreer at Kiel with a VII. My assigned grid was AM18. On my way there I had 2 succesful encounters with a small merchant and a C2 so 2 in my bag before the actual patrol! Upon reaching AM 18 i got a radio message for a convoy in the area. The weather was very bad (good for me) so i managed to reach to firing range surfaced at night without being spotted. I placed myself on the course of the incoming convoy and dived waiting. I rose to periscope depth in the middle of the convoy and the action began. I set my torpedoes at 5m as the weather was very choppy and didnt want to risk any of the eels to pass under the keel. Hit one C3 which rendered it immobile. Then 2 tankers and a liner. I dived at 130m, silent running on as the corvettes in the convoy started pinging me. After some evasive maneuvers (around 2h) they let me go (its still 1939 so they are not that good yet!). When i surface i find the damaged C3 sitting there as a duck, (0 knots as it was hit by one of me torpedoes) so i finish it off. I am out of torpedoes and i make it to base. I dock, and then the message comes out !!!!! "Ships sunk 0, tonnage 0, renown 90!) !!!!!!!

Any ideas plz? It realy p*ssed me ff
Best
VonApist