It's not surprising in the slightest. Everyone wants something for nothing. I know it's a charity and you were offering your services for free but they evidently wanted to use your ideas and keep the credit for themselves.
Slightly different situation but early last year my son applied for a position with an online food kit company and was asked for a sample recipe before his interview. He does have an extensive list of his own recipes and gave them a list of about 10 but submitted the recipes for 2.
At the interview he was asked about all the suggestions he'd made and their recipes rather than asking about his qualifications/experience. Then, just before the end of the interview they said that they'd seen him because he had good qualifications and had submitted some great ideas for future products but that they were actually looking for a woman for the job.
Over the past year, they have tried to recreate no less than 5 of his recipes, they've been a bit rubbish because he didn't give too many specifics regarding the recipes but it goes to show that if someone can steal your ideas and pass them off as their own, they will.
Why Are Blokes Obsessed With Noisy Gadgets??
Well Labour’s “patriotism” didn’t last very long, did it? 🇬🇧