Some geographic variations of C. regani have a deep beige color with a strong black lateral line but NONE of them have the well defined striations and spotting on the head that you describe. This "Spots-n-Stripes" pattern is characteristic of juvenile pikes of the lugubris group, the giant pikes from central Amazonia. Their current size (Male 6" and Female 5") only confirms that they are young lugubris. Imported C. regani are never that huge. Tank raised specimen occasionally get that big but by then, the male is old enough to get a hunch back.
I wouldn't rush to judge the reputation of your dealer yet...they simply may not have all the facts and/or they may have been shipped a bag of C. regani along with your fish and the labels could have been switched.
Some of Helen's C. regani may still be floating around in the UK somewhere. Perhaps you could track some down.
My pikes are a deep beige, with a strong black lateral