I found this at
www.uboat.net
The
VIIC/42 was designed 1942-1943 and was intended to replace the then retreating
VIIC, she had a much stronger pressure hull (with plating thickness up to 28mm) and a bit better offensive punch (16 torpedoes against VIIC's 14). Her diving depth was designed to be 200 meters with 400 meters as crushing depth (VIIC figures: 100/200 meters).
These boats would have been very similar in external appearance to the
VIIC/41 but with two periscopes in the tower as type
IX.
All contracts for the VIIC/42 U-boats were cancelled on 30 September 1943 in favour of the new Elektro Boat
XXI.
This sub was never made, it says it was designed to dive 200m with a crush depth of 400m. Maybe this is what you had seen before?