I've successfully used pre-paid VISA Cards in the past, precisely because I was worried about Facebook doing something like this (had it happen to a friend who was running a WordPress blog feat. cat videos and bought some ad campaigns using his primary credit card, then he got locked out and a nightmare ensued).

By using pre-paid cards, you limit your maximum loss in a worst-case-scenario to the amount on the card, which also you are in control of, since you know how much you want to spend when you purchase said card.

Only acceptable caveat is that the cards have about 5% fee upfront that you pay when you purchase it. (ex: 100% visa prepaid card costs about 105$). On the bright side, you can walk away from a mess like this without wasting a lot more time and money on litigation, lawsuits, cancelling cards etc etc.

Of course, for this to work, you should set limits on your spending, instead of running an endless campaign.