New MLB DH Question

[JJ]

Summer adult league, MLB rules with DH allowed. Overall rule knowledge by umpires, coaches, players is suspect. Here's what happened -

Team A presents a 9-man lineup at home plate. The PU and head coach of Team B do not notice that Team A has listed their pitcher as "P/DH". He pitches until the 6th inning, and is then taken out as pitcher. You guessed it - he comes up to bat in the 7th as the "DH".
NOW something starts to click with everyone.
The Team B coach says "He's an illegal player, so it's an automatic forfeit." He DOES protest the game at that point.
The Team A coach says, "No, you can list a pitcher as "P/DH" and keep him as DH if he's taken out as pitcher."
Umpires huddle up and say, "Well, it COULD be just a batting out of order thing."
Like I said, overall rule knowledge is suspect.
So how would you sort it out?

JJ