concernedsister,
I have been where your parents are. Shielding my addict sons from facing the music, (and maybe their bottom) and suffering the consequences of their actions.
Some days, I think I just prolonged their using, because I was practically buying the drugs for them, by giving them money, and helping them out during tough times, trying to keep them out of trouble.
Yes, your parents need to call and report the card, and money spent.
Hugs to you, and your parents, I know how hard this is.