You were wise to leave that situation. Any charity that doesn't allow people to have a copy of their paperwork to read at their leisure has something to hide. On the other hand, in this case it was most likely the person doing the accosting who was trying to scam you, not the charity itself.
If you remember the name of the charity, you might look them up on the internet. If they're legitimate, you might drop them a line or an e-mail telling them what happened. Or, if they're not there, you'll know that the whole thing was a scam.