Honestly, you will never truly know if they stole your idea, someone else at the company came up with it in parallel, or the scenario I’ve found to be most common with these things: they forgot it in the moment, then were brainstorming in a meeting later and the idea bubbled up in their mind without attribution as if it was their own, and they promptly latched on to it as proof of their own genius ;)
It stings, but unless you have standing and are prepared for the pain of a litigious stance, just take it as a compliment that the idea you came up with had merit and move on. Being possessive of your ideas is a recipe for misery, whether it’s morally justified or not. Reaching out to the company is unlikely to bear fruit if they’ve expressed no desire to have a relationship with you. C’est la vie.