The bottom line may well be that the fees get reimbursed. You lose. And I wouldn't reissue the parents a new card. I would tell them that based on your experience, they are not taking care of the card and it is very likely their family member who is doing this. You might also see if the site will provide any assistance as to how the charges are made, dates, times, period logged on, etc. (unless you have that) and ask them to see how that compares to family members access to the home PC. They should also check the PC, the cache, web browser history, etc. Who knows, they may call you and admit guilt.
_________________________
AndyZ CRCM
My opinions are not necessarily my employers.
R+R-R=R+R
Rules and Regs minus Relationships equals Resentment and Rebellion. John Maxwell