Both terms quoted don't pass the vibe check.

having a max win amount yet accepting bets with potential winnings above that amount is lazy and a scummy.

If you want to have a term like only accepting first bet on selection it should be posted on betslips and in a banner pinned to the top of all sportsbook pages.
also very scummy.

I've had some good times at Fortunejack in the past and almost recommended them to a close friend, glad I didn't after this behaviour.

I expect fortunejack to realize how horrible such rules are and offer a settlement to OP and rule changes to their terms.